When I first started with orchids, I got a beautiful Cattleya that had those markings. As time went on.... scale showed up! I believe that the place where I bought it, had treated the scale temporarily, so all that was left were the yellow marks on the top of the leaf. The scale was on the undersides sucking out the juices! Yuk! Make sure the underside of the leaves don't have any tiny speck in the middle of the yellow patch. I'm not saying that this is what the problem is, just what it could be.
