I noticed the other day that some small blue spots were appearing on my kitchen ceiling which is right underneath my bath. It just so happens that I am having a new bathroom fitted and so expected to see a damp patch on the floorboards underneath the bath, but it was totally dry.The fitter said he will take a floorboard up to check underneath. I have attached a photo, and the brown spot is where I tried to clean it off. When I smellled a spot on my finger it seemed like some sort of soap or detergent, but I can't undertstand how it's got there. The rest of the ceiling is unblemished. Anyone have any ideas please?