My suggestion is to use one of the screenshot forums - PAyware or Freeware, as appropriate - and include in the title - "Repaint".  IF there is enough traffic/submissions/interest, then *maybe* a new forum would be considered.  The catch is that any "REPAINT" prefaced submissions MUST have been made by the poster.  Otherwise, it's just another screenshot.

I propose the appropriate screenshot forum, because if there is enough interest, my opinion is that it would be added to the  in the Design Board as a "Repaint Screenshots", as it is more of a developer's showcase.