I'd just like to say that I "think" I have the same problem.
I just realized today that my WMP was red on my desktop system. It's not on my laptop or my wife's laptop though. All version 6 of avast.
I had thought that I just changed the color and forgot that I did it (I don't use that computer very often).
I'm not really worried about it though, I could care less what color the media player is. I listen to music with Winamp or via the web, and if I'm watching a video, it's usually full screen.
So, for any other Evangelists that say "It works fine for me", this isn't just user error.
However, I do think that my desktop was the only one that I didn't do a clean install of Avast on, I'm pretty sure I just did an upgrade from 5.x to 6. That might have something to do with it.
Actually, I don't even see how Avast has anything to do with this, but I guess since people are saying that it changed after their avast upgrade that it's highly suspect.