The longer I teach colour the more frustrated I become about the lack of accurate and precise language to talk about colour. It creates so much confusion.
Take the opening few lines on wikipedia for the entry on Black –
Black is the color of objects that do not emit or reflect light in any part of the visible spectrum; they absorb all such frequencies of light. Although black is sometimes described as an “achromatic”, or hueless, color, in practice it can be considered a color, as in expressions like “black cat” or “black paint”.
Well, I have an issue with the first sentence because every object you have ever seen (even the black ones) reflects light at almost every wavelength in the visible spectrum. Black objects just don’t reflect very much light. The only thing I know that does not reflect any light is a black hole. And I have never seen one of those. But it is the second sentence that I think is interesting. It essentially says (paraphrasing) that although black is sometimes described as a colour it is a colour. This does not make sense. It should read – Black is described as a colour and is a colour. Why the “Although”? The answer to this is that colour is being used with two different meanings in the same sentence.
In the first part of the sentence colour is used to define the holistic sensation of colour (colours according to this definition have at least three attributes: such as lightness, chroma and hue). Hue is whether a colour is red, green, blue, yellow etc. Chroma is how the colour deviates from grey. Lightness is about how much light is generally reflected or emitted. In short. Colours that have no chroma are said to be achromatic (grey, black, white etc.). On the other hand, in the second part of the sentence colour is used to represent that component of colour that is hue. It is only by invoking these two separate definitions of colour (the holistic and the partial) that the sentence makes sense.
There may be more than these two definitions of colour. There is also the notion that colour is used to represent the physical and the perceptual that I have raised in an earlier post.