I actually played a little game with myself this past election cycle to see if I could tell who was the GOP. I searched the names of the 2 candidates in some district I'd never heard of and went to the images page to try to guess. When both people were middle aged white guys it wasn't always easy.

I dunno, give it a shot with some house races:

TN 6

OH 12

VA 7

CO 3

MO 6