colorcount is a tool to display the colours used in a PNG image.

Why? Because indexed images take up a lot less space, but it's not so easy to find out how many colours an image uses exactly.

This should be the same as Colors ➡ Info ➡ Colorcube analysis in GIMP, just easier. Create an indexed image with Image ➡ Mode ➡ Indexed

Install with go get zgo.at/colorcount, which will put the binary in ~/go/bin.