As already indicated by Brandon, it depends on your point of view. 

If by "color" you mean the [definition you find on wikipedia](http://en.wikipedia.org/wiki/Color), 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. 

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.