Hi all. I had ceilings replastered when I moved into a house. We waited for the plaster to dry well, did a misting coat which we left to dry again and then I’ve done two coats of white paint. There are yellow patches appearing in the ceiling in all the rooms. There don’t appear to be any leaks when we looked into the attic. One room is particularly bad. Any idea why? I’ve attached a photo. Not sure how clear it is. Any help will be appreciated x