GIMP - GIMP is a multiplatform photo manipulation tool.

CODIJY Pro Photo Colorization - Add colors to black & white photos and recolor images with surprizing ease!

Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.

DeOldify - Open-source deep learning project for colorizing and restoring old images

MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.

Palettte App - Create, analyze and edit smooth color palettes