I don't know much about shielding and such stuff other than what I've read (I've got a projector). I just picked up on your moving speakers away and the discolouration being reduced.
From what I've read, your speakers, at 3-4 feet, are more than far enough away (especially given they are shielded). You could try the up, but then again it may just be the TV. Axiom says the centre channel is particularly well shielded as it is designed for placement on TV's.
I'm now thinking like the others, you may have a bad TV and best return it while the return period is in effect.
