OK so here's my crack pot theory; Keith isn't half galra He's a quarter. They've Only ever specified that he's half human, and because of his concept art of him with silver hair I believe he might be a quarter altean. The only other characters with silver hair are at least part altean, ex lotor, allura. Anything i'm missing here?
I’m willing to believe Keith is possibly galtean or from Pollux or something. But there are other galra with white hair though?? Kolivan and Ulaz, for starters. Seems to me that’s more of an effect of the rift and quintessence exposure affecting the galra over the course of 10,000 years now (like how their eyes also look gold now)