All these comments about trying to cover them up are a bit odd to me.
Can't you just remove them in settings where you think they might be visible and would rather not have them showing?
Granted, I don't know anything about nipple piercings. But I have my ears pierced and I can choose whether or not I want to put earrings in my ears or leave them "naked" any given day.
I get that you'd have to likely wear them for a bit at first so the holes don't immediately close at first...but after that why can't you just put them in and out as you please.
Again, I don't know anything about nipple piercings, so if I'm wrong about that then I apologize.