Klaus Bietenholz was an admirer of what Swiss-German artist who wrote "Writings on Form and Design Theory?"
Klaus Bietenholz:  An admirer of Paul Klee, Juan Gris, Alexander Calder, and César Manrique, his painting style has been described as "Organic-Cubism" by Dominique Vernier. Paul Klee:  Klee was a natural draftsman who experimented with and eventually deeply explored color theory, writing about it extensively; his lectures "Writings on Form and Design Theory" ("Schriften zur Form und Gestaltungslehre"), published in English as the "Paul Klee Notebooks", are held to be as important for modern art as Leonardo da Vinci's "A Treatise on Painting" for the Renaissance.
Paul Klee