Hi Michael,
Hmmmmm, I always thought that the dpi value is mainly used to calibrate screen font size.
i thought it is used to project the same sized "objects" on different amounts of pixels
You're definitely right; Anyway, some text set in a specific font may be seen as an object, the size of which has to be calibrated correctly... so nevermind, we're talking about the same thing :)
the color effects arise mostly in white fonts on black background
Did you check your anti-aliasing settings? I once had strange rainbow color effects with subpixel hinting for anti-aliasing enabled. AA without subpixel hinting gave much clearer results in my case. Check your settings in Control Center -> Appearance & Themes -> Fonts -> Configure... (near the "use anti-aliasing" checkbox). Note that only newly started apps are affected by changes. Don't try with konqueror, because it seems to use the AA settings from the preloaded instance. I always use kate, but any other non-preloaded app will do. Also try disabling AA completely. Kind regards, Michael