I don't think the issue is with painting tiles themselves, it is the fact that they are part of an open, working fireplace where the problem lies and so one wouldn't want to use a paint that was potentially flammable.
We have an open, working fire in our living room. The tiles clash with everything else in our front room. I'm thinking about painting them black. I've seen that people are refurbing their fireplace tiles using chalk paint. Does anyone know if it's safe to do this?