Which great writer propounded a "Theory of Colours"?

MC Merci, Chinese wedding dress is red , some say black/ white are only hues not colours , we could go on and on

MC Merci, And white is the colour of mourning

But you also have to consider color bias. For example, some cultures consider black as a negative color while other cultures connote it as positive. The same for red. While in the West, many use red for danger or alert, for Lakota tribes the color red connotes something sacred or holy, such as the sacred "red road" a holy person would follow. And in some Asian cultures, red is a lucky color.

astonishing that it took a writer rather than an artist to analyse colours, and so recently too.

Colors and emotions are definitely linked. He had that right. And all artists use his Color Wheel.