This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
This can happen if you forgot to put a 'p' after colour descriptor in your Windows mode definition string. For example to configure the emulator to give windows a 1024x768 screen mode at 256 colours with fully programmable colours your string should look like this:-
x1024y768c256p
Note the p at the end of the line.
 
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