We used to have a reference to 'natural grey' but I don't think any one could differentiate between it and 'grey'. It's now gone.You'd be hard-pressed to guarantee the same shade anyway, the first time wire is purchased again.
You could purposely use a different shade for your own detailed differentiation, but if blue is called for, Codes won't care about the shades, as long as it's blue. At least none I know of.
Is it "UL rated" or "UL listed?"
Is it acceptable to use two shades of blue (for 24V circuits) in a UL rated cabinet?
:lol:It is all subjective.
I described the color of my brothers house as "titty pink" and of course he relayed that information to his wife. A few weeks later she and a couple of her friends were in the alley looking at the house. Each looked down their respective blouse and said "No, I don't think so."