Some colors changes dramatically in different lighting conditions. Others do not. One can have the same color mixed with different pigments and in one lighting condition they look the same and another lighting they look completely different. This happens because the different pigments that are used in the color mix throws light back very uneven under different light conditions. The phenomenon is called metamerism. When mixing colors, you want to make as stable mixtures as possible. PaintMaker always selects the most stable solution first but also offers the unstable mixes. It is especially important to know about metamerism in figurative painting. To make a smooth gradation of, for example, a sky you must not shift pigments along the way. Doing so will give the sky ugly continuous edges under many lighting conditions.