I also liked Sheldon's list of couple costumes, and Bernadette made one hell of a Smurfette!
You know, I was kind of hoping Sheldon and Amy was going to appear as Spock and Chapel.
Nah, Spock and Uhura. More fun.
Granted, Amy-in-blackface would be, er, problematic. Although they could have just put Amy in Uhura's red outfit and let that be the joke. "My hailing frequencies are open."
Besides, Uhura is way more iconic than Chapel!