1. Color Schemer 2000. http://www.colorschemer.com/. Color Schemer 2000. http://www.colorschemer.com/.
2. Color Wheel Expert 2000. http://www.abitom.com/. Color Wheel Expert 2000. http://www.abitom.com/.
3. Goethe J. v. W. 1971. Goethe's color theory. Translated by Rupprecht Matthei. New York: Van Nostrand Reinhold Company. Goethe J. v. W. 1971. Goethe's color theory. Translated by Rupprecht Matthei. New York: Van Nostrand Reinhold Company.
4. Color2Gray