Do black holes have colour

Answer 1

Since having color would imply reflection or radiation in the visible spectrum, and because a black hole's gravity is strong enough to prevent any light escaping, the best response would be, No; thus making the "black" component of their name particularly significant.

Note that recent theories indicate that black holes can create a kind of radiation (Hawking radiation) associated with a thermodynamic interaction with the universe, but strictly speaking this occurs outside the black hole. They also have accretion disks which are highly energetic and will emit large amounts of radiation in the x-ray portion of the spectrum (the disks likely will also radiate some in the visible spectrum), and also evidence powerful relativistic polar jets which are highly luminous; but again these phenomena are outside the black hole.