It's a linguistics thing, it's about word usage more than about colour. You ask someone to get a book off the shelf, and you say "get the blue book" and the person is confused because they see a green book.

We are usually not specific in our day-to-day language, and this exposes/clarifies the issue.

I think the "numeric" equivalent to this would be "is this a few/many?"

And you would get some number arguing how "several" is a distinct category in the same way this post has people talking about cyan.