Windows 7: desktop icons suddenly changed colors

I seem to have done something that screwed up my Win 7 RC slightly, but I have no idea what it was. All of a sudden, the icons on the desktop (more precisely, icons for links, not actual files) change their colors at the last stage of the boot up. What I mean is that after I type in my password the desktop appears with all icons shown correctly. But then, as the machine finishes booting up - i.e. starts all the sidebar and anti-virus and other apps - at the last second the icons lose their colors. Sometimes later on they regain them - but again, I have no idea what causes it. If anyone has seen something similar, I would be grateful for a tip.

Try a system restore. Or delete your icon cache.

Deleting icon cache does not help - it actually helped once, but then everything became wrong again and now it does not help anymore.

Like I said before, the main problem that puzzles me is the following - during the boot process the icons first appear normal and then at the very last second change their colors. System logs do not seem to indicate what is happening at this point exactly.