Hi Ben. The multi coloured paint will most likely be Portaflek or Portatone or the more recent Aquaflek coatings. These are sprayed on and then glazed over to seal the sprayed surface. Its best to give it a bit of a sanding so the paint you will be applying can key on to it. "This is the important bit Ben". But a good quality white emulsion. Dulux or Crown from a Dulux or Crown trade centre. You can google your nearest branch. These places are open to the public not just trade. They only sell proper trade paints and not rubbish in in a bucket that says trade which you may find in some DIY stores.