I just can't resist a vintage art school color theory exercise, and strong gouache painted color delivered with precision is pretty hard to beat. Four examples here, c. 1970s--the first three completed with handwritten text labels ("analogous colors", "split complementary", etc) and protective paper laid over top, attached with masking tape to the reverses. The fourth appears perhaps to have been a first stab at what became the third (letter C)--with no labels, and slight color differences between it and the other. Signed Marion Adolf at lower right corners. 

14" x 11" each.  Gouache on heavy paper, with protective sheets still adhered over top to protect them; I flipped that paper over to photograph them, and it could easily be removed (maybe better by exacto-ing than trying to pull the masking tape off ).

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