looks like a ball anemone. I believe they turn orangish when they get bigger. usually harmless, but if they're popping up quickly they may be more annoying than anything else.
If they are in dark areas only they are ok. I can't remember their name but they are harmless and usually you get just a few of them. If you scrape it off it is gone. They are not like pest anemones that you can't get rid of.