Maybe you could key out the grey if nothing else in the shot is too grey (i.e. the actor or a shirt he or she is wearing). Just stick the clip on video track 2 or higher and add transparency, do an alpha channel and select the color you want. Then make a white bitmap or jpeg in a paint program that is 720x480 (or whatever resolution your project is set to) and import that to video track 1.
Hope this works, other than that, I don't know how it could.
Be Good!