I found a copy of Johannes Itten’s book The Art of Color at a rummage sale. Itten was a Swiss Expressionist painter influential on artists of the Bauhaus.
Itten taught about color in the face of the belief that either you were good with color or you were not.
Most instructive was Itten’s statement that, “A color is always to be seen in relation to its surroundings.” Colors shift according to their neighbors and to the light. Itten describes a mausoleum in Ravenna with blue mosaic walls, and narrow windows of orange tinted alabaster. Orange and blue are complements which means they mix into gray, and Itten says the light in the mausoleum is a magical gray, with the walls reflecting blue and orange depending on the angles.
I appreciate his assertion that mosaic art places “high demands on coloristic powers” with each fragment acting in relation to many others.