Funny, I too literally thought I had a Brown Old Mill back last week. I picked up a few Old Mills last week from an old collector and noticed two of the three looked brown. I couldn't tell for certain... I began to ask multiple people what color they thought and their decisions were split 50/50. Once I scanned the cards and compared to others I realized the Brown Old Mill backs are much more distinct in color. Also, I did some more research and found out that they are so incredibly rare that the odds of me having one are incredibly slim. After looking at the cards in various forms of light, I came to the sad conclusion that they are just very faded black.
