If you successfully design your C++ hiring criteria to be colorblind — to not notice the color of weasels, but only to notice how good they are at C++ — then performance on the hiring criteria will shadow weasel color as an indicator of C++ ability.

My comment kinda assumed that hiring criteria meeting your strict standard of colorblindness are unexpectedly hard to design. Let's say all red weasels and most blue ones suck at C++, but some blue weasels completely rule. Also, once a month every weasel (blues and reds equally) unpredictably goes into a code frenzy for 182 minutes and temporarily becomes exactly as good as a blue one that rules. Your standardized test will mostly admit blue weasels that rule, but sometimes you'll get a random-colored weasel that sucks. If you're colorblind, you have no hope of weeding out the random suckers. But if you're color-aware, you can weed out half of them. Of course it also works if a tiny minority of red weasels can code instead of none.