I find it rather bizzare that my orchid (Encyclia Serena O'Neil) is developing "patterns" on it's leaves. This one had a few thrips 6 months ago that I swiftly got rid of and the following 2 months it was pest free.
Did it develop more bugs ?
I cannot seem to notice any small beasties even with a magnifying glass.
Possibly areas that were damaged by the thrips that have become more visible as surrounding cells dried out and lost color. As long as it doesn't show up on new growth from after the thrips I don't think you have a serious problem.