Yup, I can second that. I've had the same thing happen on four legit Windows XP SP3 systems (two XP Home, two XP Pro) thus far. After updating 6.0.1091 to 6.0.1125 via the gui and rebooting, Windows Media Player turns red.
Your solution ...
regsvr32 jscript.dll
regsvr32 vbscript.dll
... resolves it and restores Windows Media Player back to the way it's supposed to look, but I don't like the thought of having to do this after every Avast program update.