8 Riso inks organized into a 3-dimensional color space. Along the vertical axis, you’ll find 3 achromatic shades - 100% black, 50% black and 15% black. Along the horizontal axis, you’ll find the parent hue at 50% opacity as well as the parent hue desaturated with 50% black.
 
To create this design, I relied on research from The Color Harmony Manual and How to Use It by Egbert Jacobson published in 1942, which in turn relied on the research of Dr. Wilhelm Ostwald who was publishing on the subject of color from 1916 to 1931.