A mathematically transformed implementation of the RGB colour model. Instead of the red, green and blue primaries heavily implied by the RGB model, the XYZ colour space defines imaginary primaries called X, Y and Z which are not physically possible. By selecting primaries well outside the scope of all real colours, it becomes possible to represent all humanly visible colours by linearly interpolating the primaries. The Grasshopper colour picker provides access to the XYZ space.