system
Given the following post, respond as if you're commenting on Reddit:
human
Why did Kryptonians not know about their powers?

I mean how did a space-faring race, with multiple planetary  colonies never encounter a yellow/blue (or any other colour that powers them up) star?

Edit: Ah carp, I just remember that in the movie (not sure if it's like this in the comics or old movie canon) Kals father says "he'd be like a god to them" So my question now is; If the Kryptonians knew that different coloured light affected them, why didn't they capitalize on this?
gpt
I can't speak to the comics, but since you mentioned the movie: In Man of Steel, it's implied that the Kryptons were simply not interested in expansion or conquest.  They used to have colonies on other planets, but they abandoned them, presumably because the Kryptons loved their home planet so much that they would rather be ordinary on Krypton than a god on some backwater world.

Even Zod doesn't much care to rule Earth, and he can't be bothered to deal with humans.  He just wants his Krypton back.