Spray each pot with pottery sealer. Let dry. Spray a colored base coat. Add designs with tape/stickers and spray again with different color. After each coat dries, remove the tape, apply a new design and spray again until you achieve your desired look. Create spattered looks by angling the spray tip. Experiment on paper first.
For a glossy surface, spray each pot with clear-coat aerosol finish. This coat will also help to protect your design from peeling or scratching.