16bit Color Depth => 256 Color Symbols

Hi,

i just changed the desktop color depth from 32bit to 16bit for some
reasons that don't have anything to do with the problem itself - and
now for most symbols the 256-color-version seems to be used,
especially the file symbols in explorer, in the quick-start-bar, and
in the tray next to the clock - but for example not in the taskbar
buttons with running programs or in the toolbars of explorer. i took
a screenshot to show this clearly:

http://www-users.rwth-aachen.de/Yannick.Berker/16.gif

does anyone have an idea how to fix this? i don't want to switch
back to 32bit if that's possible.

i'm using german windows xp sp1, if that helps.

thanks

yannick