Hi Nick.
Did you apply your new paint derectly onto the new plaster without watering it down.
For best results of painting new plater, get some really cheap emulsion from b&q, travis perkins, as long as it it a contract matt, no vinyl paint.
Water this down 2 parts paint to part water.
Now apply this by roller to all of the new plaster and don't spread it to far, one long pile roller full should do 1.5 - 2m squared and keep going back and forth over the same area untill roller is empty.
Then you should be left with very nice white, not to patchy wall.
wait till next day then apply your top colour coats.
Hope this Helps.
Joe S Dybowski, December 2009