I would agree with that entirely.
And can quote some examples that both confirm and deny it !
I've been collecting (early) poly blue Norton bits for quite some years,
and by and large they all seem approx about the same pale blue shade.
Examples of Nortons poly grey on the other hand cover quite a range of greys
- earlier examples are lighter and later are darker, and some models seem to
have a green component to them.
I'd say the Enfield grey is not quite the same, but the example I have is not in such
wonderful condition to say for sure.
If only they showed an example of the finished colour ?https://www.amazon.co.uk/Royal-Enfield-Polychromatic-Silver-250ml/dp/B00MMCTF46