If you look at the experiments that have been done, it boils down to categorizing. It's not that people (with normal colour vision) are any less able to see the

If you look at the experiments that have been done, it boils down to categorizing. It's not that people (with normal colour vision) are any less able to see the differences between colours, just that they're less likely to sort them apart unless a finer sort is needed. Test native English speakers the same way, and you'll find that they've got this "red" word that covers both scarlet and crimson (and used to cover orange as well), and a totally inadequate "yellow" that goes from something very nearly orange to something verging on green. Both of those words are more finely divided in other languages (including some "grue" languages), and the speakers of those languages will initially categorize things accordingly, where an English speaker can easily do it on a second pass when it wouldn't occur to them to make the distinction on the first.