Well, my post was supposed to be the actual reason he’s not purple, but that’s pretty much the same excuse I use in fanfics and rp and whatnot! Blue does seem to be pretty popular, though. All of Kurt’s AU kids are blue (Nocturne, Blue, Salamander, the male TJ, and Cerise),
Also, if the Draco is to be taken into consideration, some of Azazel’s “people” or whatever are blue, hence why Abyss ended up blue for that arc. It could just be that Azazel’s got the recessive gene.