The only way to change colors in a grey/black/white skin is to use SkinStudio's colorizing abilities. You won't be able to do it with Windowblinds alone. If you have SKS, edit the skin, and play with the coloring options there...I've managed to color a few grey skins to different colors. This will end up with more work though, as you will probably need to change other things like font colors, etc.
Still no guarantee that it will look good, but the colors will change.
