Color spaces! RGB, HSL, Cubehelix, Lab (CIELAB) and HCL (CIELCH).

Lab color picker

RGB color picker

HCL color picker

Sequential scales

Mike Bostock

Achromatic Interpolation

Working with Color

D3 Documentation

d3-color

Quick question: is it intentional that d3.hsl() returns a NaN value for the 'h' property if a gray hex value is entered? See for example d3.hsl('#dedede');

Stephanie Tuerk

Yes, see https://observablehq.com/@d3/achromatic-interpolation

Is it possible to get the opacity added as a 4th hex value?