Here's a link to a working version. The text is in Japanese, but hopefully, the interface is intuitive enough to grok.
The game comes from a simple math olympiad problem I found a long time ago. The idea is to invent an algorithm to make all the cells in the grid reach the same parity (color in the case of Color Switcher, key direction in the case of the math problem).
The surprising part is how little knowledge is actually required to solve the problem. Primary students with problem-solving backgrounds have a good chance of figuring it out.
Because I made the game for a Japanese content creator, there are corresponding videos for the problem and solution in Japanese.
You can download the source directly, or run
git clone https://github.com/niltnir/color-switcher.gitto create a local repository.
Open the HTML file in any modern browser, and you're good to go!