These "brown ink Recruit backs" have been known for a number of years, and may have been first noticed/recorded as such by Jay Behrens. There seems to be little premium for them, as they're not of much interest to most folks. If I recall, ones in VG/Ex quality were going for somewhere around 100-150 a while back. Every so often they get hyped and there's a flurry of activity ... then it quickly settles down - like most things T207.
It has been said that they're found with both Factory 606 and Factory 240 backs, but I've never seen images of any other than Fac 240 - at least not ones that were clearly brown. There's usually a discussion about it not really being brown, but faded black or some other nonsense as its blindingly clear in person. Once you've seen one, you can usually pick them out accurately from scans ... those that have them should know exactly what I'm referring to. There are likely lots more out there to be identified.
Someone (Jeff L?) responded to a question about whether a specific T206 Old Mill was a brown back: "If you have to ask, its not" - it applies equally here.
One of the threads David K refers to has a side-by-side of a black and brown ink back.
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Mike