A painted flower pot will be no more subject to fungus infection that a
plastic pot (which does not breathe and is thus also more subject to fungus
infection that a non-painted clay pot). However, if you do not overwater,
you should not have problems with most plants. The other disdavantage is
the paint on the exterior of a clay pot will likely deteriorate in time, and
you end up with a ratty looking pot. I like the looks of clay pots, and I
like the moisture retaining quality of a plastic pot, so I "paint" the
interior of the clay pot with black asphaltum type tree wound compound.
Works very well and lasts a long time.
Bob