Is a black hole dark?
The black hole itself is dark.
For an object to be other than black it needs to emit light. This can be internally generated light as in a star. Alternatively it can reflect light as planets and moons reflect sunlight.
A black hole can't emit light as nothing can escape its event horizon. Likewise it can't reflect light as any photon hitting it will get absorbed.
This does not however mean that a black hole is an area of complete darkness. A black hole can attract material which starts to fall into it forming what is known as an accretion disk. Particles in the accretion disk can interact with each other, the black hole's gravity and magnetic field to generate light.
In fact the brightest energy sources are quasars which generate their huge energy output from an accretion disk around a supermassive black hole at the centre of a galaxy.