painting HP Multi Jet Fusion PA12 printed parts

Anyone an idea how best to spray PA12 printed parts? The parts are not threated after printing (sanded or, polyshot). Dark colors are not a problem. If you want to spray it with white carpaint it doesn't cover. The grey tips keep coming visible untill you spray that much that everything is filled up. But also the structure is filled up then (for example a leather look). I tried several primers and spray cans but white remains a problem. Hope someone can help