Bill, it could be environmental factors but assuming that it is not I'd have them check out the following possible candidates: Arcana half-black, Nuda Localis, one of the rarer Nigra cultivars - Punctata, Othello, Fulva, Tosaensis (I think) and there is a tawny one in Europe, maybe it's the Fulva, but it is in Whittaker's new book.

Check with Mary Ann Silverman, I believe she & Burt have the Arcana half-black. I'll think some more on it.

Bill, check this one out as a possible candidate

http://www.chinabamboocentre.com/Image/plants%20images/Phy.bambusoides%20f.lacrima-deae.jpg