Here`s a puzzler: I have got a phal, Taipei Gold, that has a thin, dark similarly line down the center of some leaf "ribs." It looks like something you`d draw with a fine-tipped magic marker. It`s just on the top side of the leasves. It doesn`t wash off or rub off. Other than this marking, the plant desperately looks pretty healthy. I`ve looked in all my orchid books, and I don`t see this symptom anywhere. Is this just a normal jointly thing, or should I be worried that it has some sort of weird virus?