I'm going to play a deck with a Oko, Thief of Crowns. And my question is: can I use his abilities targeting a creature with protection from green? I know that normally I couldn't do that, because I can't even target creatures with protection from green with green spells, but for example Oko's abilities? He is blue and green, but his abilities aren't.
A creature with protection from green can't be targeted by Oko:
702.16b A permanent or player with protection can’t be targeted by spells with the stated quality and can’t be targeted by abilities from a source with the stated quality.
It doesn't matter that his ability doesn't have a color, protection cares about the color of the source of that ability. So unless you find a Thran Lens or something similar, you won't be able to target the creature.