2006 Rubicon, Detonator Yellow, 5.5" Clayton Long Arm lift, 37" Pitbull Rockers, Atlas 4:1 transfer case. Dyntrac PR60 axles (RCV shafts in front), ARB F&R Lockers, Superwinch Talon 9.5 Winch, Metal Cloak Fenders, Currie Antirock in the front, Clayton TJ skid, Genright Crawler gas tank & skid. Fox Coilover shocks in the rear. 5" WB stretch.
Alright, I'll try to give you a semi-serious response.
Keep in mind that you asked a question that comes down to a matter of personal opinion. I suspect that you're getting these sarcastic responses because most people don't think the diff covers are a feature that should stand out.
I tend to agree with that. To me, it reeks of "I'm trying hard to be noticed." From a design standpoint, I don't think diff covers are particularly attractive. So I'm not sure why anybody would try to highlight or call them to attention. For hot rods, that genre is often about showing off the modifications you've made. So if the JEep were a hot rod, I could understand why you'd want to show off the fact that you modified your gearing and/or added limited slip. But the Jeep isn't a hot rod, so it doesn't really fit the genre. In my personal opinion, on the "form vs function" spectrum, Jeeps should be biased toward function because it better reflects the purpose of the vehicle.
But if I were absolutely forced to give you an answer that is not black, then I'd chose charcoal or something subtle. I suspect that's not the answer you wanted though.
End of the day, it's your jeep. Do what makes you happy... which means this thread is pointless because nobody here knows what makes you happy except you! ;-)