I have seem something like that before, but I'm afraid to say it was on a Phal which a few months later died of a spreading hard dry black necrosis (which took several months to spread arround the crown and kill it).
I have
no idea if the white spotting was at all related to what killed it and there is a good chance it's completely unrelated.
Unfortuantely I also don't know what was the cause of either the spotting or the thing which killed my orchid
