turn the flag into a different one (preferably into something similar) - no repeats - use basic colors (full saturation + brightness (except for grayscale) and preferably a hue of an integer times 50/6) - complicated images (like the one in mexico) can just be regular images, but everything else should be vector - keep the ratio 4:3 flag log: start) usa 0) liberia 1) chile 2) poland 3) austria 4) Latvia
People having to use only your suggested colours feels restrictive. This Latvian flag for example, uses crimson instead of plain red. You disallowing that colour feels extremely disrespectful towards the Latvian community; in hindsight, Mexico with forest green, Belize with navy blue (not really though), Qatar also with crimson, Bangladesh with a really dark green, Thailand with what appears to be midnight blue, and others. If I am forced to only use your colour suggestions, an alternate segue is contained in the project to help you with that.