Colors are not purely spectral. Pink and brown are colors that must be mixtures. Black is no color. Normally I wouldn't care, but the point of article is the difference between mixtures and wavelength. The point of the post is semantics.
Some child just learning the colors gets a free pass, but if you put up a website to explain something and its wrong, I think its reasonable to "aggressively" say so.
I suspect they meant "in the spectral color space".
Claiming that it is no color in general is actually a pet peeve of mine: You're right, of course black is a color, in the right context. Colors are not singularly defined as some point across the spectral scale, where there is indeed no black and white, but can be interpreted through many other common, reasonable, and useful definitions as well.
For example, it is perfectly reasonable to define "color" as a point in a 3-dimensional space, for example as RGB or HSV triples, which are very popular and useful definitions in many contexts. Black, then, is (0,0,0).
You can also define color as an element of a particular set of available colors. If you had a "black" car, and someone asks you what color your car is, would they seriously answer with "my car does not have a color, it is black"? (Even ignoring the fact that that would most likely be a lie according to the physical definition, since the car is most certainly not perfectly black in the physical sense, but then what would you call it?)
