The point is that in English, there's still a common word for, say, both "scarlet" and "crimson", grouping them together. But there's no such common word between "red" and "green" - the latter are primary colors, always distinguished.

In other languages, that grouping is done differently, and two colors that would both be appropriate to call "red" in English don't have a single common color term at all.

To get a feel of how this looks from the other side, consider various Asian languages that don't distinguish green and blue, and have a single word that has to be translated as "green or blue" to English.