As already indicated by Brandon, it depends on your point of view.
If by "color" you mean the definition you find on wikipedia, then "black" is definitely a color; "black" is just how humans perceive the absence of any significant peaks in the spectrum of reflected light, and a low overall intensity compared to surrounding reflectors (or even a complete absence of light, like the night sky).
If on the other hand, you define "color" to be a particular (single) wavelength in the visible part of the EM spectrum (so NOT including any human interpretation), then "black", "white", all shades of grey in between, and a whole bunch of other things, are not colors; those colors do not appear explicitly in the spectrum (unless you define the combination of "red", "green" and "blue" to be "white", but then there is already a certain level of human interpretation).
There really is not a clear, unique and unambiguous answer to this question; whether "black" is a color or not depends on the particular set of base axioms you are using.