This is fantastic! Definitely bookmarking!

While I'm not one to suggest monetizing something that benefits a community I think you could reasonably monetize this by providing CaaS (ha! Coloring as a Service).

You could have weekly or monthly pdfs of generations emailed for particular themes like kids' school mascots, religious subjects like for Sunday school, curriculum subject correlating theme, etc.

Additionally, I would have it hide a signature somewhere in case someone starts scraping images and commercially selling them, or additionally license them to be able scrape them using Cloudflare.