Differently but alike, Rainbow may have + Engineering applications
not as RGB, rather for graphs and export data sets from discontinuous.
Electron is from unsourced MCD given as is [maybe not level 0.005].

Image Rainbow Colormap [RGB band].sm (29 KiB) downloaded 65 time(s).
Image Rainbow Colormap [Electron].sm (374 KiB) downloaded 67 time(s).