Color Palette Generator - Enter the URL of an image and find its color palette
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Material Palette - Generate and export your Material Design color palette
draw.io - Online diagramming application
Klart.io Colors - A data-driven collection of beautiful color palettes 🌈
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.