Well, in my opinion, the Fun Red N510 is waaaay cooler than the yellow N505, but then again I never had the yellow N505 so I really can't compare. The red ones are selling faster than the other models here in Norway, that I can vouch for :-)
Maybe it's just me but I think silver and metallic blue is being overused nowadays. They are still nice colors though :-)
Well regarding the hacks, I think we cannot expect 100% functionality on that one, maybe that is why Sony disabled them. But I do love the fact that we now have more sound options than just 1 and 2 (I love the Jazz preset) and the LINE OUT function I simply cannot live without.