I just did this when I dropped my iPad only about 12 inches onto the floor. After consulting with Apple and being told I would need to replace my screen or get a replacement iPad both for $250, I decide I had nothing to lose by trying my idea. While the iPad was off, I gently but firmly tapped each side on a hard surface. I then turned it back on...and magic! All the correct colors were restored. I think that the drop must have loosened the metal back/sides or things shifted internally. We'll see if this is a permanent fix, but it seems to be fine!