Have you ever dropped your iPad or left it in a hot car? Anything that might have caused damage to the screen or the ribbon cables leading to the screen? Could even just be a software problem. I repair nintendo DS lites for a job an I find that screens that have color issues usually have been dropped or melted.
I know this will sound weird, but bend and twist the iPad. Hold the iPad in landscape, put one hand on each side, and twist in opposite directions. (NOT TOO HARD!!!!!!!
)
Does the color change? Or does that have any effect? Try even pushing on the screen. (ONCE AGAIN, NOT TOO HARD! Only push as hard as you feel comfortable)
Shake it!
If any of that has an effect, there is physical damage to the screen, the cables, or the circuit board.