A new idea that evolved in this thread -- use the hue, saturation, value color model to generate colormaps directly with Infragrammar. While this idea is not fully developed and has had some good criticisms from Ben, I thought this proof of concept was interesting enough to continue exploring.
I used this expression in the HUE field of the HSV input (i tweaked it a bit until it seemed to use an attractive span of the color wheel):
It accepts a color value from 0-360, and allows for negative values, it seems, like -180, since it's really just an angle on this kind of color wheel:
I used a maximum value of 1 for each of Saturation and Value. That resulted in this fairly nice image:
Compare that with the build-in colormapping function Ben implemented: