I've painted them with ceramcoat,or folk art acrylic paints,then sealed with a non yellowing clearcoat varathane sealer.Held up very well.Have also decoupaged some and sealed those the same way.

Almost ditto, although I've used artist-grade acrylic paint (Golden and Liquitex), gesso once when I thought I'd need it (I didn't, acrylics stick just fine without it), some mural-grade acrylics (so they're hues [not necessarily the authentic color due to price] and don't contain the pigment density of artists' colors, but also don't cost what artists' colors do), the occasional iridescent, and some polymer clay (which had to be bonded with superglue as the pots Did Not Like being heated and cooled like that).

I've done this on terracotta and clay, sealed and unsealed. Acrylic is a very forgiving and versatile paint.

Acrylics and polymer clay technically don't need to be sealed, but will certainly be more durable if you do, so I'll second using any finish of Varathane or any other varnish you like that's clear and untinted.

Varathane is an old favorite of mine that i use everywhere, although I will say it's not listed as outside-durable (although it does very well outside for extended periods) and some colors (phthalo blue that I've noticed as it's a favorite of mine) will fade badly in a year or so of direct sunlight even behind a window.

I might suggest a UV protectant under the Varathane for pots that will go outside or in a windowsill as I suspect that any organic color you use, including the phthalos, and certainly any of the napthols, will fade very badly in sunlight. Note that all those colors are Lightfastness I (Excellent) or II (Very Good), but none are intended for use in direct sun.

I've even ruined some paintings that get an hour of sun a day due to the phthalo blue bleaching out over a year or two. The blue sky I painted turns misty and cloudy. :-)