CKWB - As much as I don't like bright yellow - I was thinking the same thing for S3. S1 was blue, S2 was Red, I thought S3 should be yellow. They could have made it a nice yellow.
Anyway, if I'd gone with yellow for S3. I would have gone with Black for S4. For one thing, Clark looks stunning in black...

and he wears that Black Kryptonian outfit in S4. Plus black is just an awesome/classy color in my opinion (okay, I know it's not really a color, but absence of color, but go with me here...) They could have had the Daily Planet background and stuff in gray. I think that would have looked real classy.
(I did actually like the gray okay, but on some discussions I read, some people absoutely hated it)