Thanks. No it doesn't - just alters the colour of text in plain windows.
Rebooting the PC gave me proper text on the desktop, but not the special white "shadowed" desktop text font that you can read against any picture in the background. There are other problems too: the little graphics in some of the pages in Gmail etc don't get displayed at all. This happens with Firefox but not with Microsoft Edge - perhaps there's a sinister reason for this.
I get the impression that the "High Contrast" setting is very much still in development. What it provides that I really want is a clear contrast between the current window and the others. (Important if you have a number of programmes running which have different keyboard shortcuts). Anybody any ideas how this can be achieved without all these problems?