Black holes are black because mathematics is deemed useless in defining their properties.
Black holes, i would submit, are the 'top of the hierachy' in the orbital tree ( star family ) .
Black holes also orbit ' a master black hole' - this is a cosmic nature law. A hierachy of orbit.
I would also submit, black holes are dark bue to energy acceleration - exceeding the speed of light
is why we dont see anything - its too fast to be visible electromagnetic radiation.
Magnetism and gravity work hand in hand in the centre of galaxies.