In theory if it were possible to do so and one could paint a black hole would it look like an enormous smooth ball or would its surface be rough and strewn with debris?

Answer 1

As you say, in theory, if it were possible.......

This is the heart of the matter. It is not really possible. But as an analogy, if you think of a whirlpool, you can't see or paint that either, what you see and can paint is the effects of the whirlpool on water and things floating or living in the water and their behaviour as they are attracted to and sucked into the whirlpool.

A black hole is a place of infinite gravity where even light cannot escape - so there is nothing to see. But all known and observable black holes have a huge accretion disk where the matter and energy being sucked in speeds up to incredibly high speeds and covers vast areas of space.

The black hole in the centre of our galaxy is not active (feeding) and has no accretion disc but can be observed by the very odd behaviour of the stars around where the black hole is believed to be.

I hope this helps a bit.