An implementation of the luma-chroma colour model, strictly speaking defined as a transformation of the XYZ colour space. The Y axis represents the luminance, while the x and y axes encode the chrominance aspect of a colour, although not in as obvious a way as the a and b axes in the L*a*b* colour space. When plotted at a constant Y value, the Yxy space yields what is commonly called the CIE Chromaticity diagram. In the Grasshopper colour picker the chromaticity diagram is based on the Yxy space.