XyY

From ColorWiki

The xyY color space is a transformation of the CIE XYZ color space onto 2 dimensions.

This allows the illustration of color using a graph like the Chromaticity Diagram and it removes the luiminance component of color.

The formulas for determining xyY are as follows:

x = X/(X+Y+Z)
y = Y/(X+Y+Z)
Y = Y