There are several variations of this theme in existence:

• http://www.neurobiologyofaging.org/article/S0197-4580(09)00296-6/
• http://www.mathworks.com/matlabcentral/fileexchange/26026-bipolar-colormap
• http://www.mathworks.com/matlabcentral/fileexchange/24870-fireice--hot-cold--colormap

I made one using bezier curves to reduce banding:

It does have a sharp angle at the midpoint causing a black band for 0, but that's intentional because it's for diverging data. (would be best with #1806) Here it is with a wavelet scalogram:

Like Ged Ridgway's, the midpoint brightness can be changed, with gray for surface plots, etc:

and color order flips if midpoint is brighter than gray:

Would this be good for inclusion, either as a (cleaned-up) function or as a single fixed map?