Today, while I was attending an honors banquet, a girl in my class and her boyfriend were arguing over whether or not black was a color. When she had somewhat convinced him that it wasn't (I say somewhat because the argument was more-or-less ending and he didn't have a rebuttal), I asked "Wait, are you saying I can't paint with black paint?" She conceded that, of course black paint can be used to paint with, but that black wasn't technically a color. At which point I explained that we were likely using two different definitions of color, and that we should explain what we mean. I gave two definitions: 1] The various shade which a human eye was seeing and the brain was processing. 2] The specific wavelength of light that a human eye can pick up. The boyfriend and I were using definition 1, where as she was using definition 2. And with that cleared up, the debate ended.

Note: Both definitions aren't word for word, but somewhat close. I was simply making the distinction between the wavelength itself and the process of seeing something and placing it in a certain color category.