Question--is there a reason you're mainly considering flushed ships for Karkat? Because while there's a good question of whether he's really capable of that kind of hate, he does spadeflirt around a lot, especially with both John and Jade, and I'm pretty sure either of them might be willing to pretend it's totally black just to save Karkat the vapors over his own moral turpitude. :)

Also the idea of trolls pinging humans as kind of androgynous appeals to me greatly--both for kink purposes, and because it could potentially reinforce any racism in the greater society (assuming it struck other, less accepting humans as sort of weird/uncanny valley-ish).