Here's a puzzler: I've got a phal, Taipei Gold, that has a thin, dark
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 leaves. It doesn't wash off or rub off. Other than this marking,
the plant looks pretty healthy. I've looked in all my orchid books, and
I don't see this symptom anywhere. Is this just a normal thing, or
should I be worried that it has some sort of weird virus?