The Munsell color space was invented by an artist named Albert Munsell in the early 1900s. It breaks color down into three dimensions: hue (or color family, like red, yellow, green, blue, and purple); value (darkness to lightness), and chroma (intensity). Any color may be precisely described by specifying its hue, value and chroma.
It provides a very simple language for describing color with perfect precision, and a conceptual model that makes it simple to understand.
The Wikipedia page on Munsell is a great place to start learning about it. Check back to this page shortly for more information.