I can't remember specifically (barely paid attention in art class from like 8 years ago) but I know that yellow + purple = bleh to me.

I had to chuckle at that. Yellow and purple are actually complimentary colors on the color wheel.

That said, I don't think there's actually a yellow/purple stone drake. There's a green/purple one? Which is a bit "eh" in my opinion too, but. I like the others, I think. Especially the one from Vortex Pinnacle (the white/blue).