This time it is about colors. There are many color theories. The theorie from Itten is the one I'm talking about. We actually need only three colors to paint in all other colors, those colors are called primary colors. So Itten invented the color wheel. This is a small circle with the colors bleu, yellow and red. It is surounded by a larger circle with the colors you get by mixing those three colors. For example, between bleu and yellow you get green. And between red and bleu, purple.
the color wheel of Itten