The goal of this project is to develop a color space transformation technique that adapts the color space to the color of the illuminant and leads a new color representation that is more independent of the illumination intensity and is more adapted to the spectral composition of the illumination than any of the existing approaches. The central notion of our new color space transformation scheme is that it aligns the vertical axis of the new color space with the color of the illuminant in the original RGB color space. This provides us two benefits: 1) Locating the vertical axis of the new color space in the direction of the brightness of the illuminant color gives us the adaptation need to achieve color constancy; and 2) The project of the pixel data onto the horizontal plane in the new color space provides us with a single scalar descriptor for the chromaticity -- as opposed to the two such descriptors that would be needed otherwise with two-dimensional color subspaces, such as the HS color subspace and the rg-chromaticity space.