yemihikari
The younger paladins, after getting back together, discuss human-alien hybrids.
Disclaimer - I don't own Voltron. There are quite a few theories floating around regarding Keith having alien DNA, but one of the theories doesn't really pan out.
Note - One of the theories I've come across is that Keith, as a Galra-human hybrid would have purple skin, but also have the ability to camouflage the fact he has purple skin. However, the camouflage ability is an Altean ability, not Galra. Keeping this secret wouldn't have been easy, particularly back on Earth, but when Pidge revealed herself to actually be a girl, that would have been a good point for Keith to reveal he was Galra-human and had purple skin, as they as a team was supposed, to be honest with each other. It makes more sense if Keith is part Altean or Galra that he doesn't know. Thus no purple skin, or other oddities.