It seemed logical that you could also set cookies from Agents, like so:
Print "Set-Cookie: style=contrast; expires=Friday, 11-Jan-2030 01:10:00 GMT; path=/;"
Give it a go and see what you think. The high-contrast colour scheme might not be exactly what a visually challenged user would like, but you get the idea. Store most CSS in a global.css file and then all those that govern colour and other aspects of appearance go in other CSS files.
I should mention, the other side to this is in the computed $$HTMLHead field where you add the following code:
"<link rel=\"stylesheet\" href=\"styles/" +@Middle(HTTP_COOKIE; "style="; ";") +".css\" type=\"text/css\">"
I know I promised that database for download today, but I keep thinking of new things to add to it, whereas I should be tidying up the code to the point where I'm happy to release it. I go away next Wednesday for a week, so that now is my deadline to make it available. I might try and squeeze some more goodies in before then...