A color reader on its own: pick one and read it in hex, RGB and HSB, or edit it with the sliders in whichever format you like. What you pick here stays here — Pin keeps it in Pinned below, and the palette never hears about it. To build a palette, use the color in the Palette section instead.
These copy colors into the palette below. They don't change the site's colors.
Or pick the background color
The color above is the background, exactly as you picked it, and the rest is built from it: the surfaces are short steps off that color, and the muted tone, the text and the highlight are pushed until they read on top of it. Whether the palette comes out light or dark is decided by the color. Start from copies any of the site's palettes in here — Green, Blue, Pink — in its light or dark variant, and you edit from there. Change all rebuilds the rest without touching the background; Edit each color lets you type any hex by hand; Copy takes all eight colors as text. Save keeps it in the list below — leave the name blank and it's filed as Palette #hex of the background. These palettes live on this page; they don't change the site's colors.
Pinned colors live in this browser. Paste one or more hex colors into Add a list of hex colors to pin them together. Download .md takes them out as a readable list, → Notes drops that same list in as a new note, and Copy puts it on the clipboard.
For when you have a color in one format and need it in another, or want to keep the ones worth reusing.