Where does “Gelb” come from?

Gelb (German) comes from Middle High German gël, from Old High German gelo, from Proto-West Germanic gelu, from Proto-Germanic gelwaz, from Proto-Indo-European ǵʰelh₃wós, from Proto-Indo-European ǵʰelh₃- — to flourish; green, yellow.

Gelb (German): yellow; yolk