Albert Munsell’s color system definition

Munsell created a numerical color notation system that rested upon the five colors of blue, purple, green, yellow and red.  The original sphere is made up of ten pure hues around its perimeter.  When colors are combined with white they turn into tints, and they move up the vertical scale.  When they are combined with mixtures of black, they are positioned further down the scale, and become shades.  In addition to moving vertically, the colors move horizontally toward the sphere’s center, and change gradually in purity as they turn into neutral gray tones.