It's not a good idea to paint a cage with any kind of paint since it is going to be bit off anyways.
All types of paint, no matter how non toxic, is not a good thing in an animal's stomach.
From your point of view and the bird's point of view, a painted cage makes it harder to see both in and out and think of the bird's mental health. It's hard enough to live in a cage so try to make it as large and unobtrusive as possible.
Personally I don't like the idea of keeping a bird in prison all it's life.