[rvense]

> But to me it feels like the major divisions as we know them in English are intuitive beyond language.

Did you perchance grow up as an English speaker, or a speaker of a language with a set of colour terms similar to English?

> Surely when you look at grass and the sky you feel you need different terms to describe them

Well, I'd guess that all languages have different words for sky and grass. The difference is how you relate those words to words for other things that have similar colours. There are many languages with less colour terms than English, but also some with more - and as far as I remember it's usually green and blue that have more shades, if you'll excuse the pun. Like the slice of spectrum covered by green-blue in English will be covered by more words in some languages.