A standard RGB-based color scale and a rainbow color scale.

ROOT: TColor Class Reference

3 Very Different Color Models: RYB, RGB, and CMYK - Color Meanings

Are the colours of the rainbow analogous to a musical scale? - Quora

Learn How to Choose Right Heatmap Colors Palette

Some reflections and experiments - VWG – Output Transforms - Community - ACESCentral

Color Issues

Color Wheels are wrong? How color vision actually works – @ASmartBear

python - What is a good palette for divergent colors in R? (or: can viridis and magma be combined together?) - Stack Overflow

D.3 Basic R colors Data Science for Psychologists

Information Visualization and Color - This view of service management

The Book of Shaders: color

ggplot2: Elegant Graphics for Data Analysis (3e) - 11 Colour scales and legends