For painting concrete pots, I would advise using an exterior acrylic paint such as Dulux Weathershield. It's suitable for masonry and can be tinted to a variety of different colours. This is a self-priming paint, so there is no need to prime separately.
Using Crommelin 750ml Ornamental Sealer outside or inside the pot before painting will ensure the paints' longevity. This sealer will prevent water permeating through the concrete and trying to push off the paint that you've applied. - MitchellMc