Rotatable hue angle?

[endolith]

Current colorscheme make sense if you remember ROYGBIV:

• R = positive real numbers
• Y = positive imaginary numbers
• G = negative real numbers
• B = negative imaginary numbers

but I could also see a mnemonic for G = positive and R = negative, due to G = Go and R = Stop, and similar to color scheme used in things like http://www.falstad.com/circuit/ or http://www.falstad.com/membrane/