Het hypo means he carries half the hypo gene. Where pastel is also half of the gene, but still shows because it is co-dominant, het hypo is non visual because hypo is recessive.
To take advantage of the het hypo, get a female that is either already full on hypo for the best odds, or another het hypo and hope you hit the odds.
Use world of balls' genetic calculator to see what those odds will be, and to see what % het the babies will be.