re: iPhone 4 replacement screen help

Yeah, they are easy to screw up. Even a nick in one of the tracers in the ribbon cables that's hard to see with the naked eye can cause problems with discoloration, distortion, intermittent touch response, etc. That, and excess pressure on the LCD component from warping, piece of broken glass stuck in the phone housing, etc.

Or, like Gaston said, could just be defective screen. I've installed a couple dozen of them from various sources and haven't had a defective one yet, but most of them are cheap aftermarket knockoffs made in China, so it's not a big stretch of the imagination to consider some of them might be broken right out of the box.