Colors is free to use and shows no ads.
I spent over 100 hours developing it so if you want to reward my work and help me keeping Colors ad-free please help covering the server costs.
I originally made Colors for the German competition "Jugend Forscht" when I was 13 years old. 2018 I wrote a huge upgrade while still keeping the old version available. Additionally the source code is now public: feel free to fork, open issues and make some push requests on GitHub!