I have a yellow/greenish screen tint too, but there is a 3-step workaround:
1. Jailbreak
2. Download 'Color Profiles'
3. Manually adjust Color Temperature, Gamma und White Levels until you're satisfied. It will take a while, but it pays!
I have a georgous screen now, with perfect whites and amazing colors. You can tell the difference by a mile and you won't get such a screen out of the box, no matter how often you exchange!
PS: There are no yellowish 'defective' screens. Every single screen has a more or less different screen tone. You can get rid of the yellowish/greenish tone by adjusting the second slider (RGB -> 1. Red, 2. Green, 3. Blue) at Gamma and White levels in Color Profiles.