Definition
The CIE 1931 color space was conceived in 1931 to represent all colors that can be perceived by the human eye.
It can be represented in 3D space with the R, G & B values in coordinates, but is often represented in 2D, where it looks like a rounded triangle.
It is not perceptually uniform, contrary to the [[CIELAB color space]]
! X, Y & Z =/= R, G & B