graphics/py-spectra: Color scales and color conversion made easy for Python

Spectra is a Python library that makes color math, color scales, and
color-space conversion easy.

Support for:

Color scales
Color ranges
Color blending
Brightening/darkening colors
Saturating/desaturating colors
Conversion to/from multiple color spaces

Spectra is built on colormath and grapefruit. Spectra is enormously inspired by
chroma.js and d3's scales.