Thank you for sharing these images.
I am aligned with other comments about the challenges of identifying colors; Its near impossible given the age of stamps, scanning inconsistencies and subjective elements. The only sure way to know is to have the stamp on a cover and have the cancel date as a definitive guide. But of course your stamps are loose. Its an annoying and frustrating thing for these particular (and other stamps)
With all kind and due respect, I'm not sure I agree that the references to a U.S. publication is directly related because these are Newfoundland stamps--but of course I get the general point.
Let's look at Walsh's Newfoundland Specialized Stamp Catalogue:
This "Prince of Wales" issue was engraved in 1880 and there are 3 known colors at that time:
Violet brown (1880)
Gray brown (1880)
Deep brown (January 1896)
In addition, many proofs in black, green, etc.
There was also a green issue of same 1 cent PoW from 1887 to 1896--with 4+ other known shades but that is a whole different thread or pandoras box
Here are my best stamps of these issues, for sharing and possibly comparison...