Professor Albert H Munsell created the Munsell colour system. It is a colour space that separates colour dimension into 3 areas; hue, value and chroma.
Hue measured by degrees around the horizontal circle. Each horizontal circle is divided into 5 principal hues: Red, Yellow, Green, Blue and Purple along with 5 intermediate hues – which is halfway between each principal hues. There are now in effect 10 sub colours (red, yellow red, yellow, green yellow, green, blue green, blue, purple blue, purple, red purple). Within the 10 sub colours there are 5 hues = in total there are 100 hues separated in increments of 2.5.
Value measures the lightness; black (value 0) at the bottom and white (value 10) at the top. There are several colour solids and gray gradient in between.
Chroma measures the purity of a colour (saturation) with the lower chroma being less pure and appearing washed out, otherwise known as pastels.
Munsell colouring system is also referred to as the number theory. By identifying each colour with a universal number we can produce an accurate representation and of the colour pallet.