Actually, they were all black. Anything else resulted from fading and weather.
Interesting. I'm not certain about absolutes of style over the time period from, say the late 17th to the end of the 18th century. And there were may have been regional differences in regard to "acceptable" styles. Certainly there would have been class differences in the approach to style, although perhaps that entailed more conformity among the rich, with quality and trim rather than individuality being indicative of status, and more necessity driven choice among everyone else, with availability, affordability, and fitness for purpose driving hat selection rather than conformity with style. It would be an interesting sociological investigation with lots of confounding elements.
The National Archives offers this information.
Black, grey, and “tobacco,” or tan, were popular choices for the hat’s body color.
https://prologue.blogs.archives.gov/2014/08/18/hats-off-to-the-tri-corner-hat/
Geo. Franks, Hatter claims to make period accurate hats, and offers some of his reproductions in colors other than black (but no red hats.)
https://cockedhats.com/products/bound-ramillies-style-fur-felt-cocked-hat
https://cockedhats.com/products/bound-wool-felt-cocked-hat-with-liner-no-cockade
This page cites a fashion history book,
Fashion, Costume, and Culture: Clothing, Headwear, Body Decorations, and Footwear Through the Ages, by Sara Pendergast, Tom Pendergast, and Drew D. Johnson, editors, as saying, "Generally dark in color, tricornes were often edged with a gold braided trim after about 1675." (I'm not sure about their use of the term "tricorne.")
https://fashionhistory.fitnyc.edu/tricorne-hat/
This forum's own .54 ball had this to say on the subject nearly 10 years ago:
Now there are paintings of Brown, Tan, green, grey and white. These are rare and seem to match an outfit. Some of these images appear to be everyday folk but most appear to be wealthy. Sometimes these are from the Empire/Regency/Federal period when a Major Fashion change occurred.
In closing, there is evidence for other colors besides black and that's fine; I have a brown one, but I think if one is serious about the 18th and early 18th Century, you need to have a black Sunday go to meeting/militia/business hat.
https://www.muzzleloadingforum.com/threads/tricorn-hat-color.94107/
I have looked at a lot of 18th century contemporary paintings lately, and I can't find one red hat.
I did find this, but it's a modern work.
https://americanart.si.edu/artwork/homme-au-chapeau-rouge-22033