Artist 
Writer Otswald color system
The Ostwald color wheel has eight colors and is based on how the eye sees color. The human eye sees four colors, red, yellow, green, and blue. This wheel has four primary colors: red, ultramarine blue, sea-green, and yellow. The four secondary colors are: orange, purple (ultramarine blue and red), turquoise (ultramarine blue and sea-green), and leaf green (sea-green and yellow).
See the Color Building Block for more information.