There's 16 different shades, or colours, there. If I was to point to any one of them individually and ask my young children what colour it was they'd almost certainly say "blue". And I'd understand them fine and consider it correct. Likewise if they were explaining something they saw during the day and said it was "blue" I might make an assumption about which of these shades it was, but I intuitively know it could have been any of them. And most of the time the distinction isn't that important for understanding and sharing experience.
When the distinction is important my kids would probably simply say "light blue" or "dark blue". Additional adjectives will get used to clarify the relative difference between the colours.
Soon they'll learn "sky blue", "baby blue", "navy blue". Then teal, turquoise, aqua, cyan, cerulean, etc.
Assuming the language has those words. That only occurs when the need to distinguish is common enough to established a shared understanding across a large enough group of people that they effectively reach a consensus that it's now a thing, like English speakers did a few hundred years ago with the introduction of the colour orange. Nobody invented a new colour, we started using a new word to describe something that had always been.
I read a book a few years ago called Alex's Adventures in Numberland (https://www.amazon.com.au/Alexs-Adventures-Numberland-Alex-B...). In it he has a story about a group in South America who have no words in their language for a number greater than two (or maybe it was three? It's been a while since I read it). Anything larger than that was just referred to as "many". It's not as though seeing more than two of anything was uncommon, most families would have a half dozen to a dozen children. But if you asked how many children they had it was just "many". Whether it was eleven or twelve just wasn't an important distinction to them.
He goes on to discuss how language can expose what's important to a group and shape thinking. The introduction of a concept and word for zero was hugely important for our advancement in all number of fields. He also discusses how our constant pursuit for ever increasing levels of specificity has it's trade-offs: we seem to be becoming increasingly bad at estimating (which is both language, social expectations around what we value, and a reliance on tools).
Anyways, it was a story about language and numbers that I thoroughly enjoyed.
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.
That probably depends on how frequently do you need to describe something as "sky-colored" vs "grass-colored". I can't really think of many things in nature that are blue (some people's eyes, the occasional flower or gemstone) so if you don't need that word to describe anything else you might just leave it at "the sky is a weird shade of green" rather than having a color that only describes one thing in the universe.
https://www.paintersmategreen.com/
It stands out against cardboard and all the variously-colored plastic boxes I own, and it's light enough to offer great contrast with a black Sharpie on it.
So for me, that color is useful specifically because it's relatively unique.
FWIW, in Italian the sky is commonly referred as 'azzurro' (azure), except when it really is a deep blue, while a blueberry would definitely be 'blu' (blue). So, yes, in Italian we tend to distinguish the two colors more than, for example, english. Which I guess is the point you are making.
Sometimes maybe. Most of the time, who cares? Grey, clear or dark skies seem most important to distinguish. Do we mean the temperate daybreak blue, midday tropics blue, or depth of full moon night blue? Grass and other plants can have degrees of blue in there too. What about sea? Sometimes blue, sometimes green, most of the time somewhere in between. What probably matters most to a mariner is swell and temperature(?).
I suspect it only really started to matter after Perkin's mauve in the mid 19th century, and matters far more now in a world of a trillion pantone shades.