Do you know of any quizzes that test for that kind of perception? I know I'm not colorblind, but I strongly suspect I'm lacking the color-combination-preference circuit.

Sure, grab the nearest girl ask her if your clothes match. If she laughs you fail.

Ok just kidding :) Although girls do generally have more sensitive eyes than guys, so its not totally silly.

I am under the impression that my clothes mostly match by default, since all my pants are khakis. I just imagined some set of images that I was supposed to compare for appealingness, and then have a hidden set of answers I could compare to; that would demonstrate it pretty strongly for me, without having any power of suggestion involved.

Khakis are so great for that. The best part is, girls see hundreds of douchey guys wearing jeans and something that doesn't match. It's a strong clothing choice for like 15 different reasons.