Codec Problem - B/W playback

I installed and unistalled several time the latest codec pack and nothing helps: if i play the file by double clicking it, no matter what player i use (wmp, media player classic and others) it always comes up in black and white.
only after i process it with GSpot it plays correctly.
What can i do?
I use xp sp2. i cleaned my registry twice and used the standard installation.
Thanks

You might want to check the overlay settings on your video card. It’s usually under your display settings, somewhere under advanced.