Is black a color?

It depends on your perspective. Scientifically, black is the absence of any colour. It's what you get when all colours are subtracted. In that sense, black isn't a colour. It's "no colour". However, in art and fashion, that's largely irrelevant because it's still a distinct type of thing of the class of things we call colours.

It's a bit like the argument about whether zero is a number or not. You could say it's not a number because it doesn't have a value; zero is the thing you have when you specifically don't have numbers. But you could also say it exists and is necessary, useful and even visible by absence. How many giraffes are in your room? Zero. You can see your room is giraffe-less just as you can see something is colour-less (or black).