Hugh

Depends - are you talking perception or physics?
http://en.wikipedia.org/wiki/White_(color)
White is a color, (more accurately it contains all the colors of the visible spectrum and is sometimes described as an achromatic colorââ‚ƚ¬Ã¢â‚¬ÂÂÂ�black is the absence of color) that has high brightness but zero hue. The impression of white light can be created by mixing (via a process called "additive mixing") appropriate intensities of the primary colorspectrum: red, green and blue, but it must be noted that the illumination provided by this technique has significant differences from that produced by incandescence (see below).

http://www.city.ac.uk/colourgroup/faq.html#faq3
In terms of Perception, Black like Greys and White, is an achromatic colour: a colour without hue and saturation (or "strength").
If the term is intended to be Physical (physical and psychophysical concepts are often confused) and Black refers to a total absence of visible radiation (light) then, if there is no physical stimulus, there can be no physiological response: no response-> no perception-> no colour.