d3/d3-color: Color spaces! RGB, HSL, Cubehelix, CIELAB, and more.
Colour Tools
cccolor: HEX, RGB & HSL color picker l
fantastic ms. (@fox@front-end.social)
LCH Colour picker
Material Theme Builder
Muz.li Color Palette Generator
Pigment
Color Names
npm: nice-color-palettes
ColorSpace - Color Palettes Generator and Color Gradient Tool
Colors - A nicer color palette for the web.
Tilda Colors. Color palettes for your website.
Color Combinations
Color Contrast Checker
Palx