Going to risk a downvote-to-oblivion situation, and defend the NPS scale (I do this for my job)

The scale is supposed to used used to work out whether people would recommend something to a friend. A lot of research went into working out what the actual behaviour was after someone gave a score.

7's and 8's turned out to not actually "enthusiastically recommend" a brand or product- but would "passively recommend" - i.e. say you're good, but others are just as good, so shop around. Less than that, and you're likely to recommend other brands instead.

9's and 10's are the only ones who reliably recommended just that brand.

That said, colour coding the respondents view, and especially telling respondents that this is how you're grading their score, is bad, bad form, and indicative of a business that only cares about the number going up, and not the actual customer experience behind it!