I'm sorry you haven't been able to get a good one. Having been there myself, I know how frustrating this is.
I am one that believes most PW's suffer from the color hue issue to varying degrees and if you're sensitive to seeing the hues, you may be better off waiting for the next version of the PW to come out and see how that is.
It sounds like you talked to a rep who was clueless about the problem. I have been lucky to talk to a rep that is familiar with the PW color hue defect, but it was still very difficult for me to get a good one.
I suppose you could try a 4th replacement, but I don't think you'll end up happy at this point. I think it's best to return it for a refund and maybe get the basic kindle for now. Good luck with whatever you decide.