Working on cataloging all of my T cards, and while going through my T206 stack I found a Southern Leaguer Old Mill that appears to have a Brown Back. I'm familiar with the theory that these were scrap created by using the ink from a Hindu sheet and were never actually released in packs. The miscut and oversize top/bottom of the card would seem to fit with this, but Westlake (as far as I know) doesn't exist with a Brown Hindu back.
I don't have another Old Mill to compare with, but I've compared to other ATC/American Lithography sets and it certainly looks Brown to me, distinctly different from the black. Is their a better way to identify a Brown Back? Here's the card:
https://imgur.com/a/IKnnZ
Thanks for any insights you experts have! I've learned more about vintage baseball T sets browsing here than I would have ever thought possible.