Anyway, in these discussions I came across an open access BAMS paper discussing a shift from the traditional RGB color scales to an updated Hue-Chroma-Luminence (HCL) color scale. So here is a short blog post on how to use this technique with GrADS.
Link to paper: BAMS HCL paper
The paper includes a link to an online tool used to generate HCL color scales, with an option to output into GrADS RGB format. So below are a couple of examples of GrADS figures using HCL color scales
Link to the HCL Wizard: http://hclwizard.org/
To access the HCL creator, just click on the link to the Online HCL Creator. From there it should be pretty easy to follow, simply pick your color scale, and set the export option to GrADS. It takes a little time to figure out how to use the sliders, but you'll get the hang of it.
A couple of examples from the GFS:
Other color science resources:
Some good information how to use color in your figures: http://betterfigures.org/
Color Brewer, another website with color scale creation, and modification: http://colorbrewer2.org/