What is the name of that beauty? I grow outdoors in South Florida so my experience may not be of any help. I have occasionally (but not often) had a leaf turn yellow like that. Sometimes it's just from physical damage. I would cut off the leaf and, unless it spreads, I wouldn't worry about it. That's a very healthy looking vanda. Good luck.
it just a combination of waterspot/sun/fungus damage. Nothing to worry and happens on all vandas. Vanda are very tough and resistent to fungus, but all have occasional leaf drop or damage in the middle part.