Dither it! VS Shrink Me

Maybe it will be overkill for flags, but you can try with dithering algorithms, where you can select which color you want to keep: Https://ditherit.com/ Https://github.com/noopkat/floyd-steinberg. Source: over 1 year ago

ImageMagick can do anything, but it's a commandline program. There may be some websites that dither images for you - https://ditherit.com/ is one. (I also wrote a program years ago that is excellent at color reduction and dithering, but it's not currently usable.). Source: over 1 year ago

It’s called dithering. Instead of using many different colors you just choose a few and make the best of it. With using six colors (red, green, blue, yellow, white, black) any color can be matched. You can try it out with this tool: https://ditherit.com/. Source: almost 2 years ago

I used https://pixelartselfie.com/en. I later found https://ditherit.com/ which offers more features so I’ll probably do more works. Source: almost 2 years ago

Check this website: https://ditherit.com/. Source: almost 2 years ago

Shrink your maps' data before uploading: https://shrinkme.app/. Source: over 1 year ago

2) shrink your map sizes (I always use this site: https://shrinkme.app/ as it retains resolution but drastically reduces size),. Source: almost 2 years ago

And then I use this web site to shrink the file. I can't tell a difference from the original to the shrunk webp Https://shrinkme.app/. Source: almost 3 years ago

Hi! Omatsuri is a web app with some CSS and web optimization tool (https://omatsuri.app/), and shrink me is an image optimizer (https://shrinkme.app/), always in web app form, I use mint webapp to make them as a standalone program. Source: about 3 years ago