Windows 11 December Preview Triggers White Flash in File Explorer Dark Theme

Windows 11’s December preview update has introduced an ironic new hazard for dark‑mode devotees: File Explorer can briefly flash a bright white screen — a literal “flashbang” — after installing KB5070311, and Microsoft has acknowledged the problem while engineers work on a fix.

Background / Overview​

Microsoft released KB5070311 as a non‑security preview cumulative update on December 1, 2025, paired with a servicing stack update reported as KB5071142. The stated intent of the package is to extend and polish dark‑theme coverage across File Explorer and a number of legacy dialog surfaces so Windows 11’s dark mode feels consistent and less jarring during common file operations. The update targets Windows 11 builds 26100.7309 and 26200.7309, and Microsoft’s official release notes list the File Explorer visual changes alongside a short “Known issues” section that explicitly documents the white‑flash regression. The change is a welcome one in principle. For years, File Explorer and other legacy Win32 dialogs sometimes defaulted to bright white even when the system theme was Dark, producing high‑contrast interruptions for users working in dim environments. KB5070311 aims to remove those mismatches. But in the process of modernizing paint/order and theming older UI paths, a timing‑sensitive regression was introduced that can expose a white background briefly before the dark UI finishes rendering. Independent reporting and community reproductions confirm the symptom and match Microsoft’s description.

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What users are seeing: symptoms and reproduce points​

The bug’s behavior is simple to describe and easy to notice in low light: when Windows 11 is set to Dark mode and File Explorer is opened or refreshed, the main Explorer content area can display a bright white screen for a fraction of a second before the dark content paints. The white flash is short, but intense — users have described it as camera‑flash‑fast to as long as a second on some machines. Microsoft lists the specific actions that can reproduce the white flash:

• Launch File Explorer (including launching directly to Home or Gallery).
• Create a new tab in File Explorer.
• Navigate to or from Home or Gallery.
• Turn the Details pane on or off.
• Select “More details” while copying files (expanding copy/move dialogs).

In many reproductions the ribbon and navigation pane remain dark while the central content area flashes white — a pattern consistent with a paint‑ordering or compositor race rather than a total theme failure. The behavior is intermittent: some systems never show the flash, some trigger it occasionally, and others reproduce it reliably on each action.

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Microsoft’s official position and timeline​

Microsoft’s support article for the December 1, 2025 preview explicitly records the white flash under “Known issues in this update” and states engineers are working to resolve the issue. The support page also explains how the update is packaged (LCU + SSU) and gives guidance for removing the LCU portion if rollback is necessary, noting that the SSU component generally cannot be removed once installed. That guidance is important for anyone considering uninstalling the preview while waiting for a patch. There is no permanent, documented user‑side workaround published by Microsoft at the time of writing; the vendor’s public guidance is limited to acknowledging the problem and promising a fix in a future update. Given the optional preview nature of KB5070311, Microsoft’s practical message to most users is implicit: treat this as a test build and avoid broad production deployment until the Known Issues entry is cleared.

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Why this probably happened: a technical analysis​

Styling legacy UI surfaces to match modern dark themes is not a one‑line color swap. File Explorer is a composite of modern XAML/WinUI surfaces and long‑standing Win32/COM code paths. Extending dark palette resources into those legacy paths changes the window creation order, initial paint timing, and the way frames are handed off between the application, the Desktop Window Manager (DWM), and the GPU driver. If the first visible frame clears to a default background (historically white) before the themed content is fully initialized and painted, users will see a brief white frame.
Key technical factors that make this brittle:

• Desktop Window Manager and GPU driver handoffs schedule frame composition; a late theme application can expose a default background for one frame.
• Mixed rendering stacks (Win32 + XAML/WinUI) have different initialization and paint lifecycles; aligning them is non‑trivial.
• Third‑party shell hooks, theme injectors, and driver idiosyncrasies can alter paint order and make race conditions more likely on some hardware. Community reports indicate larger or HDR/OLED displays and certain GPU driver versions seem more prone to visible flashes; those correlations remain anecdotal until Microsoft publishes root‑cause telemetry. Flag: treat hardware correlations as unverified community observations unless Microsoft confirms them.

This phenomenon is a classic painting/timing regression: a desirable functional change (making dark mode consistent) altered the render and initialization sequence enough to occasionally expose the white default background on the first visible frame.

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Scope, variability, and what we don’t yet know​

The issue is demonstrably real and acknowledged by Microsoft, but several aspects remain open:

• How widespread is it? Microsoft’s Known Issue entry confirms the regression exists but does not publish telemetry scope or percentage. Independent media and forum reproductions show it’s intermittent and environment‑sensitive.
• Which hardware/drivers are most affected? Community reports point to higher likelihood on certain GPU drivers, external displays, and machines running third‑party UI injectors, but this is anecdotal and not vendor‑verified. Mark these claims as unverified until Microsoft issues a technical postmortem or driver partners publish confirmations.
• Could other apps be affected? In theory, any app that mixes legacy and modern rendering paths could exhibit similar timing artifacts; at the moment the documented issue is confined to File Explorer. Administrators should nevertheless be alert for other visual regressions after installing preview builds.

Where a claim cannot be verified from Microsoft telemetry or an authoritative vendor statement, it will be labeled as anecdotal and discussed with caution in this report. Community testing is valuable but should be treated as supplemental evidence, not definitive proof of a universal failure mode.

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Accessibility and real‑world impact​

A short white flash might sound trivial, but it has tangible accessibility and usability implications:

• Photosensitive users: Sudden high‑luminance spikes can be painful or dangerous for people with photic sensitivity. The community raised this concern early and rightly pressed Microsoft to prioritize remediation.
• Low‑light workflows: Creators working in dim studios, night‑shift operators, or those who rely on dark mode to reduce eye strain will experience repeated jarring interruptions.
• Helpdesk burden: Cosmetic regressions drive support calls. For large organizations, a spike in “the machine flashed white” tickets could significantly increase workload and create confusion on whether the problem is a security event.

Given those impacts, the risk is not purely cosmetic — it is a user‑experience and accessibility regression that merits urgent attention and a conservative rollout posture for administrators.

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Practical mitigation: what you can do right now​

There is no single magic workaround that preserves dark mode while fixing the paint ordering at the OS level. Microsoft’s support article lists no permanent user workaround other than rolling back the LCU; however, practical mitigations exist and have tradeoffs.
Quick, safe options for home users:

• Do not install KB5070311 on machines where a consistent dark experience is required. The update is optional and preview‑oriented; skipping it is the easiest way to avoid the problem.
• Switch to Light theme until a patch is available. This avoids the dark‑mode paint path that triggers the race condition, but it defeats the purpose of using dark mode. Steps: Settings → Personalization → Colors → set Default Windows mode and Default app mode to Light.

Rolling back the preview (more advanced):

• Open Settings → Windows Update → Update history → Uninstall updates and look for the KB5070311 LCU entry. Use the GUI uninstall if available.
• If the combined package prevents GUI uninstall, use DISM to remove the LCU package only:
• Open an elevated Command Prompt.
• Run: dism /online /get-packages (identify the LCU package name).
• Run: dism /online /remove-package /PackageName:<exact‑LCU‑package‑name>.
• Reboot.
  Caveat: DISM operates on the component store — use with caution and verify system health first (for example, DISM /online /cleanup‑image /scanhealth). The SSU is generally not removable once installed.

Community mods and runtime patches exist that attempt to intercept Explorer paint timing; these can restore a dark visual experience quickly but carry security and stability risks and are not suitable for managed fleets. Use at your own risk and avoid on devices that require strict supportability.

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Recommendations for IT administrators and enterprise teams​

For production environments, adopt a conservative, methodical approach:

• Pause optional preview updates in production rings; treat KB5070311 as test/pilot only.
• Add KB5070311 to a small pilot ring that represents the variety of hardware profiles in your environment (OLED/HDR, discrete GPUs, common driver versions). Validate Explorer workflows and accessibility requirements there prior to any wider rollout.
• Update helpdesk guidance and KBs with symptom descriptions, mitigation steps (switch to Light theme, uninstall LCU via Settings or DISM), and a clear rollback plan.
• Monitor Microsoft’s official support page and release notes for the fix and for any follow‑on guidance from GPU vendors. Apply the fix in pilot first and then proceed with normal ring deployments.
• Capture and submit reproducible logs and short screencasts to Microsoft (Feedback Hub) if you encounter consistent reproductions; this speeds diagnostics and prioritization.

Prioritize accessibility: if you manage users with photosensitivity or similar conditions, treat this as a blocking issue for rollout until Microsoft clears the Known Issues entry.

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Alternatives: which File Explorer replacements to consider​

If the white flash is intolerable and you want a dark file‑manager experience immediately, there are third‑party and open‑source alternatives that can substitute for File Explorer. Caveat: replacing the default shell or introducing third‑party file managers has operational tradeoffs (integration gaps, support overhead, potential security considerations). The most commonly discussed options:

• Explorer++ — a lightweight, open‑source file manager with tabs and a classic Explorer‑style UI. Actively maintained on GitHub and distributed under GPL‑3.0; can be run portably or installed. It is not a drop‑in replacement for all Explorer shell behaviors, but it’s a solid light‑weight alternative for many power users.
• Files (Files Community) — a modern, touch‑friendly, open source File Explorer alternative that aims to provide a modern UI with tabs, previews, and themeing. Community builds and Insider releases are available; user experiences vary and performance differences have been reported in some configurations (test before deploying). Community projects carry the usual caveats (support, update cadence, telemetry differences).
• XYplorer (commercial) — a mature, feature‑rich file manager favored by power users. Not open source, but a stable paid alternative with a long history. Consider this for advanced workflows that require robust features and supported releases.

When evaluating alternatives, test these points:

• Dark theme fidelity and absence of the flash symptom.
• Integration with your file share and enterprise policies.
• Performance on your typical hardware.
• Supportability and update cadence (critical for managed fleets).

If you choose a third‑party manager for individuals, do not replace Explorer broadly in a managed estate until you can validate security posture and user training.

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What to expect next and how Microsoft is likely to respond​

Given the severity from an accessibility and UX perspective, there are two realistic remediation paths:

• Microsoft issues an out‑of‑band cumulative or targeted patch that corrects paint/timing ordering for File Explorer dark mode; or
• Microsoft bundles the fix into the next scheduled Patch Tuesday after additional validation.

Which path Microsoft picks depends on telemetry severity and the complexity of a robust fix across GPU vendors and third‑party compositors. Historically, timing and composition regressions often require coordination with driver vendors and compositor adjustments, so a thorough fix may take several test builds and validation cycles. Meanwhile, Microsoft will update the support listing with status and remediation details when available.

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Final analysis — balancing progress with polish​

KB5070311 is an important step toward a more cohesive dark mode experience in Windows 11: extending dark palettes into legacy File Explorer surfaces addresses a long‑standing usability complaint and — when it works — improves comfort for night‑shift users, creators, and people with ocular sensitivity. But the white‑flash regression is a blunt demonstration of the engineering tradeoffs involved: modernizing deeply embedded UI code paths can introduce brittle timing regressions that erode trust and create real accessibility risk.
The appropriate short‑term posture is conservative: treat the December preview as a pilot, avoid broad deployment in production rings, and prefer either deferring the update or using the Light theme in sensitive environments until Microsoft publishes a tested remediation. For power users who insist on the immediately available dark improvements, test on non‑critical hardware and be ready to roll back via Settings or DISM if the flash proves disruptive.

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Checklist: immediate actions (condensed)​

• If you are a home user who values a stable dark experience: do not install KB5070311.
• If you already installed it and the flash is unacceptable: switch to Light theme or uninstall the LCU (Settings → Windows Update → Update history → Uninstall updates) or use DISM to remove only the LCU component.
• If you manage devices: pilot the update only on representative hardware, update support templates, and block or delay optional previews in production rings.
• Capture logs and submit reproducible feedback to Microsoft (Feedback Hub) if you hit the bug frequently; include short screencasts to help prioritize the fix.

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The white‑flash bug is an instructive reminder that cosmetic improvements can have outsized operational and accessibility consequences when they intersect with decades of legacy rendering behavior. Microsoft has acknowledged the problem, the company’s support documentation explains the symptoms and rollback mechanics, and a fix is in progress — but until that fix ships, dark‑mode users who cannot tolerate sudden white bursts have sensible, conservative options: defer the preview, switch to Light mode, or test alternate file managers on non‑critical hardware.

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Source: XDA Dark mode users, beware: a Windows 11 bug is causing File Explorer to flashbang people

 

[ChatGPT]

Microsoft has confirmed that a recent optional preview update can cause File Explorer to briefly flash a bright white screen when the system is set to Dark Mode, producing jarring flashes during routine actions such as opening folders, creating new tabs, toggling the Details pane, and more.

Background​

Microsoft shipped the December 1, 2025 preview update identified as KB5070311 (OS builds 26200.7309 and 26100.7309 for Windows 11) as an optional quality and UI update intended to make File Explorer and several dialogs more consistent with the operating system’s dark theme. That same release, however, includes a documented known issue describing a regression where File Explorer can momentarily display a blank white screen when dark mode is enabled. The preview package was published ahead of the regular Patch Tuesday cumulative releases that follow Microsoft’s normal servicing cadence; this is the kind of optional, “preview” roll‑out that is aimed at early adopters and test channels before broader deployment to production machines. Media outlets and community trackers that tested the preview confirmed the same visual regression and reported inconsistent but repeatable reproduction in multiple environments.

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What Microsoft officially says​

Microsoft’s support note for KB5070311 lists the symptom in plain language and enumerates the specific Explorer interactions that reproduce the flash:

• The File Explorer window may briefly show a blank white screen before the UI and folder contents render when the system is in Dark Mode.
• The problem can occur when you: navigate to or from Home or Gallery (including launching to Home), create a new tab, turn the Details pane on or off, or select “More details” while copying files.

Microsoft’s current guidance is that the company is working on a resolution and will update the support article when a fix is available; no official workaround is provided in the support note.

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How the bug appears in practice​

Independent reporting and community testing add detail to the way the visual regression presents itself:

• The white fill often covers the central File Explorer content area, while persistent UI elements such as the navigation pane or ribbon may remain in dark colors. This mismatch makes the white flash especially noticeable.
• The flash can be frequent for some users (appearing on every Explorer open) and sporadic for others, indicating variability across hardware, drivers, and user configurations.
• Reports from early adopters show the symptom on both 24H2 and 25H2 installations of Windows 11 after installing the preview build numbers Microsoft published for KB5070311.

Community threads and testing logs suggest the regression is visual only — Explorer’s functionality (copying, moving, deleting files) remains intact — but because it involves a sudden, bright flash on displays that are otherwise dark, the user‑experience impact is high for those who use dark themes habitually.

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Technical reading: what likely went wrong​

The symptoms point to a rendering or theming regression in Explorer’s dark‑mode painting pipeline. In plain terms, when Explorer initializes or repaints parts of its UI, the new theme-aware elements appear to be painted in a sequence that briefly exposes a white background before the dark theme layers are applied.

• This kind of regression commonly results from changed drawing order, a missing background brush for a particular control, or a timing difference between compositor and application paint passes introduced by an LCU/SSU combination.
• Reports from community testers mention interaction with GPU drivers and third‑party shell extensions, which can alter how and when Explorer is composited to the screen; this helps explain the variability between systems. However, no single third‑party driver or extension has been identified as the root cause and Microsoft’s bulletin does not attribute the issue to a specific driver or vendor at this time.

This analysis is necessarily tentative: Microsoft has not published a technical post‑mortem or a code‑level explanation. The diagnostic evidence available publicly is limited to symptom descriptions, community telemetry, and how the bug reproduces across different actions in Explorer.

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Who is affected — scope and severity​

The issue is confined to Windows 11 systems that have installed the KB5070311 preview package and are set to use Dark Mode. The Microsoft advisory references both 24H2 and 25H2 servicing branches by calling out the corresponding builds. Reported real‑world impact so far is:

• End users who set Dark Mode as their preferred appearance and who open File Explorer frequently will notice the regression regularly.
• Users with large, high‑brightness displays (OLED panels, HDR‑capable monitors) or those working in dimly lit environments will likely find the flash more intrusive.
• People with photosensitive conditions — such as those prone to visually induced seizures — could be at elevated risk of adverse effects from sudden, high‑contrast flashes. Bright, unexpected flashes are a known trigger for photosensitive seizures in a small proportion of people with epilepsy and can cause headaches, dizziness, or discomfort in others; for that reason, minimizing unplanned flashes is a legitimate safety consideration.

From a security standpoint the defect is a user‑experience regression, not a vulnerability. It does not, based on current public information, allow code execution or elevation of privilege; the principal harm is visual disruption and potential health discomfort for sensitive individuals.

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Immediate mitigation: what affected users can do now​

Microsoft’s official support note does not present a formal workaround other than saying it’s resolving the issue. Community and editorial guidance highlights a few practical mitigations you can apply today:

• Switch to Light Mode (quick and effective)
• Open Settings > Personalization > Colors.
• Under “Choose your mode,” pick Light.
  This avoids the dark‑mode painting path that triggers the flash, but it is a blunt trade‑off for users who prefer dark theme aesthetics.
• Uninstall the preview update (roll back)
• Open Start > Settings > Windows Update > Update history > Uninstall updates.
• Locate the KB5070311 cumulative package and uninstall it, then restart.
• If the package does not show in the UI, use DISM or wusa with the appropriate KB ID to remove it from an elevated command prompt: wusa /uninstall /kb:5070311.
  Note: uninstalling updates may remove other fixes bundled in the same package; test before applying broadly.
• Pause optional/preview updates
• Do not click “Download & install” for optional updates in Windows Update until Microsoft issues a fix. For IT environments, hold the preview release in WSUS/SCCM or use update deferment policies until the bug is addressed.
• Alternate file managers
• If the flash is intolerable and switching system theme is not an option, some users temporarily use third‑party file managers (Explorer++, Total Commander, etc. that don’t follow the same Explorer painting path. This is a workaround, not a fix, and introduces support/security considerations tied to the third‑party package.
• Driver troubleshooting (experimental)
• Anecdotal reports indicate GPU driver interaction may change the flash frequency. If you suspect a graphics driver exacerbates the symptom, try updating to the latest official driver or testing a rollback in a controlled way. This is environment‑specific and not a guaranteed remedy.

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Step‑by‑step: safely uninstall KB5070311 (concise)​

• Back up important data and create a system restore point.
• Settings > Windows Update > Update history > Uninstall updates.
• Select the KB5070311 entry and choose Uninstall. Reboot when prompted.
• Verify Explorer behavior and, if satisfied, pause optional updates to prevent automatic reinstallation.
• For managed fleets, decline/hold the preview in WSUS or software update management tools and document the reason for deferral.

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Advice for IT administrators and help desks​

This regression is the type of issue that underscores why preview updates exist: to catch regressions before they reach broad production rings. IT teams should treat KB5070311 as an optional preview and follow conservative rollout practices:

• Pilot in a small, representative ring before wider deployment.
• Update test matrices to include dark‑mode, high‑DPI, multi‑monitor, and mixed GPU environments.
• Prepare helpdesk scripts that describe the symptom and offer immediate mitigations (switch to Light mode, uninstall preview package).
• If your environment supports it, block or decline the optional preview package in WSUS or Intune until Microsoft confirms a fix.

Document the rollback path and ensure support staff understand how to reverse the installation if users report the flashing behavior.

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Health and accessibility considerations​

Although the white flash is a UI regression rather than a security vulnerability, it raises real accessibility concerns. Sudden, high‑contrast flashes can provoke discomfort and, in a small subset of the population, may trigger photosensitive seizures. The Epilepsy Foundation and related medical consensus advise caution around strong flashing stimuli: frequency, brightness, contrast and how much of the visual field is occupied all affect the likelihood of an adverse reaction. Users with photosensitive conditions should avoid exposure to unexpected flashes and take precautions such as switching to Light mode or uninstalling the update until the issue is resolved.

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What to expect next — timelines and uncertainty​

Microsoft’s support note says it is working on a resolution and will update the article when more information is available; no ship date for a fix was published at the time the advisory went live. Several outlets and community trackers have observed that the preview was released on December 1, 2025 and that Microsoft’s regular Patch Tuesday cumulative release for December is scheduled in the company’s normal servicing cadence — some reporting points to December 9, 2025 as the likely Patch Tuesday target for the cumulative LCU. Whether the December cumulative will include a fix for the Explorer flash is unconfirmed and should not be assumed; customers who cannot tolerate the regression should defer installing the preview or uninstall it until Microsoft publishes a resolution. Marking the Microsoft support page for updates and revalidating on Patch Tuesday is the pragmatic approach. Note: any suggestion that this preview is “the last major update” for a future year or that it finalizes a release cadence for 2026 should be treated carefully — those statements are speculative and not documented by Microsoft. Where timelines matter, rely on Microsoft’s own update notes and the official release channels for confirmation.

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Strengths and risks of Microsoft’s handling (critical analysis)​

• Strengths
• Microsoft published the issue openly in the KB support article and listed reproducing steps — transparency that benefits IT ops and power users who depend on documented known issues.
• The preview update mechanism exists precisely to catch regressions like this in optional channels so production environments can avoid unintended disruptions.
• Risks and weaknesses
• Shipping a visible dark‑mode regression in a UI update undermines confidence in the overall dark‑theme rollout, especially after Microsoft positioned the release as a consistency improvement for dark mode.
• The lack of an immediate or documented workaround in the official note leaves end users with only blunt options (switch theme or uninstall preview). For people with accessibility concerns, that is a shortfall.
• The variability of the symptom across systems increases support costs; intermittent, hard‑to‑reproduce visual regressions require more diagnostic time and complicate helpdesk resolution flows.

In short: Microsoft followed good practice by publishing a support note, but the visible user impact and lack of a fast mitigation reduce the practical benefit of that transparency for affected users right now.

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Final takeaways and recommended actions​

• If you are on a production machine or manage a fleet, do not install optional preview updates like KB5070311 until Microsoft confirms the fix; treat them as intentionally experimental.
• If you have already installed KB5070311 and the white flash is unacceptable:
• Temporarily switch to Light Mode, or
• Uninstall the KB via Settings > Windows Update > Update history > Uninstall updates.
• For help desks and IT admins: pilot, document, and hold — ringed deployment policies exist to prevent precisely this kind of user‑experience regression from reaching critical endpoints.
• If you or users in your organization are photosensitive or have epilepsy, err on the side of caution: avoid exposure to unexpected flashes and follow medical guidance on minimizing risk.

Microsoft’s support page will be the authoritative source for the status of the fix and any future workaround the company provides; until that update appears, the measures above are the most reliable ways to avoid the white‑flash regression in Day‑to‑day use.

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Conclusion
Aiming to make dark mode more consistent across Windows 11, the KB5070311 preview instead introduced a high‑visibility regression that briefly exposes a white screen in File Explorer for Dark Mode users. The issue is disruptive and potentially harmful to visually sensitive users, and Microsoft has acknowledged it and pledged a fix. In the meantime, conservative update hygiene — deferring optional previews, piloting in controlled rings, and using documented rollback steps when necessary — remains the recommended path for users and administrators who require stable, predictable behavior from Windows 11.

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Source: gHacks Technology News Microsoft warns: File Explorer may flash with a blinding color in dark mode - gHacks Tech News