[Daub]

What books I would recommend would depend upon what application you would put them to. User Danwills mentions color spaces, which are the means by which colour is expressed and also the means by which color is 'transcribed' from one device to another. For this I would highly recommend Kuehni, R.: Color Space and its Divisions: Color Order from Antiquity to the Present. Wiley-Interscience, 2003. A great read.

It sounds as if you have an interest in the aesthetic application of colour. The standard tomes are Itten's The Art of Colour and Goethe's Colour Theory. In my opinion, both of them are semi-incoherent messes that have done more harm than good to painters. Bruce McEvoy's website 'Handprint' evidences a man who knows more about colour that Itten ever did. https://www.handprint.com/HP/WCL/water.html Its good to see that he is finally getting round to writing a book.

The way I teach color application to my students is broadly as follows.

Firstly, the 'thinking' color space for an artist (digital or traditional) should be Hue, Saturation and Lightness (HSL). Using these values the colors of an aesthetic image can be 'conceptually disassembled'. To demonstrate this, I ask my students to describe the colors they are each wearing in terms of pairwise comparisons of HSL (e.g. 'A' is the same saturation as 'B' but of a different hue and slightly lighter).

For lightness, the simple rule of thumb is to ensure that the tones are approximately separate into three bands: light, middle dark (LMD). To this one might add black and white as the top and tail. Of courses, there is not an absolute rule, and without even blinking I could show you painters who have successfully employed only two-tone bands. Novices tend to overload the lower end of the tonal range. To demonstrate tone organization, I draw a posterise curve on Photoshop's Curves. It is important to know that the M of LMD is not absolute (with M as 50% with 0 as black), but instead tends to lay around 40%. It can also be observed that most paintings extend from black to white. However, again without even trying I could name a dozen exceptions (for example, check out the low tonal range of some of Gwen John's painting).

Saturation is the intensity half of the chromatic component of colour. In common with lightness, it exists as a 'ramp' value bound by a min and max. For this reason, it can mostly be treated in much the same way as lightness. For most of art history, the saturation map of a painting followed its lightness map. It was the development of the chemical and dying industry in France that introduced artists to a wider range of intense pigments. The saturation map of Gericault's Still Life with Lobsters is remarkably different to its lightness map. If you don't have access of MATLAB or Nuke or suchlike, you can make a saturation map in Photoshop using the Selective Colour adjustment. Just cycle through the colours in the drop-down menu and set the black value of each one to -100%. For the white, neutral and black, set the black value to +100%. Seeing the saturation of a painting expressed in this way is something that the impressionists would have murdered for.

Hue is the difficult beast in the HSL triumvirate. To get a grip on it you have to side-step into the RYB colour space. It is in the RYB colour wheel that the hues are arranged in their perceptually antagonistic pairings: red/green, yellow/purple, blue/orange. These pairings have been know for 100s of years, even before Newton's colour wheel was a thing. It is uniquely difficult to get a handle on hue... it defies easy conceptualisation. There is also a huge amount of bullshit in the wild on the subject of hue. Check out adobe's colour wheel: color.adobe.com/create/color-wheel See all that stuff about triadic complementary etc? Most of it is mostly hot air. How do I know? I have personally reviewed the hue histogram of hundreds of paintings. From this I can say that the organisational strategies that artists employ are, at best, approximate. Certainly, they are not as clear as the art books tell us. However, the following is generally true... painters avoid: hues that span no more than one half of the RYB hue wheel, hue that are evenly distributed on two halves of the RYB hue wheel, hue that occupies 360 degrees of the RYB hue wheel.

The final key wisdom that I expect of my students is to understand contrast as a structural phenomenon. This can be understood as manifesting in two (main) ways. The first is ratio contrast, which is simply the contrast between two values. In painting, these values are usually averages. Separately considered can be the contrast between neighbouring regions and those which are not. The former are perceptually prime and can overwhelm our ability to perceive those regions which are distant to each other. The second contrast is global contrast. An image which extends from black to white has higher global contrast that one which extends from dark grey to light grey. These two ways of understanding colour contrast can be extended in many dimentions. For example, the way that they manifest between (ratio) and within (global) the depth planes of a landscape.

As for what constitutes effective colour contrast: one observation holds true of all painters, writers, filmmakers etc.: that their task is to exaggerate life. This they do in two dimensions: exaggeration of difference and exaggeration of similarity (though Ruskin expressed this as a difference between affinity and contrast).