Here's another simple program I've created that creates color-by-number mosaic patterns and lets the user fill in each cube with a different color.
This program was created using vanilla JavaScript, HTML, and CSS. It uses the Google Fonts Zilla Slab (https://github.com/mozilla/zilla-slab) and Quicksand (https://github.com/andrew-paglinawan/QuicksandFamily). It's hosted on Netlify (https://www.netlify.com/)