Die K Desktopumgebung

15.2 How do I change the color depth?

AFAIK, there's no way you can do it on the fly. You can either start X using:
 startx -- -bpp ??
where ?? can be 8, 16, 24 or 32 depending on the depth you want, or if you're using xdm/kdm, you'd have to edit /etc/X11/xdm/Xservers (may vary) by putting:
 :0 local /usr/X11R6/bin/X -bpp 16
for color depth 16.

Alternatively, you can edit the XF86Config file and add a line like
 DefaultColorDepth     ??
to Section "Screen". The next time you start X, it will run with the newly-configured color depth.