CIE Space-Why?
nCIE = Commission Internationale de l’Eclairage (International Lighting Committee).
nNeed way to describe colors precisely for industry and science
nWant to describe all visible colors in terms of three variables (to get 3D coordinate space) vs.
infinite number of spectral wavelengths or special reference swatches…
n
Not going to get into how this space was devised, but Photoshop's Lab space is a CIE space and Photoshop uses it as a way to translate between different color “modes”: RGB, CMYK, grayscale…

This useful for showing why, no matter how much effort you spend color matching, some colors will never look the same printed out as on the screen. Monitor gamut, in blue, much large than printer gamut. Film much gamut than printing,


From Foley, van Dam