Goethe painted this small wheel in watercolours and captioned it in 1809. It presents the core principles of his colour theory in the form of a circle less than seven centimetres in diameter. In his representation of the colour spectrum, the secondary colours “blue-red”, “yellow-red”, and “green” appear between the primary colours red, yellow, and blue. Goethe also attributed specific human characteristics to the colours and different intellectual and emotional faculties to the gradients. This was how he explained the “sensory-ethical effect of colours”.