For what it's worth --
The T80 Cairo Monopol that Ted posted used to belong to me, but I traded it to him while keeping another one that I still have. Here are scans of the backs of the two cards side by side, with the one that's now Ted's on the left and the one I still have on the right:
The ink on the right one looks maybe a little darker than the ink on the left one (Ted's), though it's not a dramatic difference, and scans can be deceptive. I just pulled out that card (the one on the right) and looked at it under a bright light, and I could definitely see it as dark brown. However, under the same bright light it's definitely darker than the ink on my T206 Broad Leaf 350, which in turn is noticeably darker than a Hindu (both pictured below). The Cairo Monopol is more brown than the ink on my better black Lenox (or the Cycle 350), but not as noticeably as the Broad Leaf or the Hindu.
So, the results are ambiguous, but I thought I would throw in my two cents.