I got paint on a white leghorn by accident this summer... she still has it on her. I've used it in the past as an ID method (paint on the tail of birds I saw in the nest box) and it lasted until the next moult.I've tried marking birds with blukote and despite the way it can stain feathers, and everything else, it didn't last long even on a light colored bird.
Anything you 'paint' on a bird they will try to preen off and thus ingest, so be careful.
I've seen folks use nail polish on toes and legs, didn't last long..and again, I don't want my birds ingesting that.
A guy recently cut the feathers of a cockerels tail in half to ID him, that would work until molt.