I WANT HUE provides a compelling UI, using sliders to guide towards a color palette. This tool displays the end color palette as HEX and RGB values, pre-formatted for either JSON or CSS for easy copy/pasting into your tool of choice. Inspired by Chroma.js and ColorBrewer.

Credit: Mathieu Jacomy

CHROMA.JS color-palette helper is a go-to resource for previewing sequential color-steps and pulling the HEX codes for them. Overall, Chroma.js is an essential tool for visualizations that utilize JavaScript (click here for the full project page).

Credit: Gregor Aisch