ColorBar is an interactive ColorFunction designer for Mathematica. It allows you to easily modify existing color functions, change colors or vary the blending fraction and get the final result in other applications. You can also use it directly inside a plotting function.
Can create a continuous diverging color map starting from any two RGB colors, by converting to linear-RGB, then XYZ, then CIELAB, and finally into Msh, a polar-coordinate version of CIELAB. These color palettes are useful for visualizing data where both large low and high values are interesting, with a well-defined midpoint.