olour names are of great significance perceptually, yet are very hard to put bounds on scientifically. And there are some hues where the name is ambiguous: yellow-green for example. And all the while, aside from those people who have severe colour deficiency everyone knows what red is, what yellow is, what green is, and these perceptions are of great significance in our interpretation of an image.

It is complicated by the issue of colour constancy – see my page Colour Constancy Intro – where the eye might perceive a colour as red, say, in the context of its surroundings, yet the same colour, surrounded by white, would be unequivocally identified as brown. Though never yellow, wherever you put a red, it will never look yellow, nor will it look green or blue.

So we have some immutable named hues, that cannot be induced to look like any of the others whatever you do, though any of them can look to have a different name under varied conditions.

■ Red can look brown (dark red) or pink (light red) or orange (yellow-red) or magenta (blue red).

■ Yellow can look brown (dark yellow) orange (red yellow) and yellow-grey (low-saturated dark yellow).

■ Green can look yellow-green or green-cyan or green-grey (low saturated dark green).

■ Blue can look cyan (green-blue) or purple (red blue) or blue-grey (low saturated dark blue).

And in each case of these variations on the basic hue, there are gradations, there’s no one yellow-grey for example, in fact there isn’t really one anything.

And yet, these hues, though nebulous, are significant for the visual perception. Or rather they are, but not in isolation, they are in relation to the hues and brightnesses that surround them.

My page Colour Name Modder is interactive code designed to allow experiment with named colours – distilling an image to a limited set of colours in order to examine how mood or emotional effects might be ascertained from the colour-named clues, and how technically, by modifying the colours, mood or feel may be altered.