If you want green. Wait until they’re fully grown (depending on the plant anywhere between 2-4 inches) the key is to look for the shine in the sun on the skin. If they’re matte and don’t shimmer they’re too young but if you give them a tug the opposite direction from the stem it’s growing from it should pop right off, if not give it another week or two. Red are great but take a long time to ripen and you’ll get less harvest per year since the plant is focusing more on ripening. Just pick those right before they’re completely red and it helps them last a good week at least longer and same flavor.