CIE Standard Colour Matching System and CIE Standard Colour Chart

The Tristimulus values can be normalized into the so-called standard color components or standard chromaticity values, x and y, as follows:
x = X / (X + Y + Z) ; y = Y / (X + Y + Z); (z = Z / (X + Y + Z))
Since x + y + z = 1, z does not need to be explicitly calculated, because it is given by: z = 1 – x – y.

These values are usually represented in the CIE Standard Color Chart in the x-y plane, which is also referred to as the “shoe sole.”
A specific color value is uniquely defined by the values Yxy, with the addition of the brightness Y.