RE: Darkening font-lock colors

[Drew Adams]

> I think it would be useful to have the possibility to change 
> Emacs visual
> appearance by changing all faces settings simultaneously. 
> This could be done
> using the GTK color selector to adjust global HSL. These 
> values could be
> saved/restored for different situations or tastes. Is there something
> similar? Anyone would like to contribute?

I don't know what that is, so I don't know if it's similar, but Do Re Mi lets
you change all faces at once. 

You can increase/decrease any color attribute (for all faces) incrementally:
red, blue, green, hue, saturation, value (brightness). You can thus modify
either the foreground or the background of all faces at once. Once you see what
you like, you can customize to the current values.

http://www.emacswiki.org/cgi-bin/wiki/DoReMi

See commands `doremi-all-faces-fg' and `doremi-all-faces-bg'.