My baby turns purple head to toe

My 10 month old son started turning purple at the beginning of February. On this face his nose, cheeks,round his mouth and sometimes his lips turns purple. On his body his hands, arms, under his finger nails, legs, toes and sometimes his torso turns purple. He does this any were between 1 to 3 times a week and sometimes twice in a day. I have not found a doctor yet that can dignose it for me. He does not appear to be in any distress or being having any trouble breathing when he does this. It can last any were from 1 to 3 hours at a time. He was born 6 weeks premature and had a heart condition that has since checked out fine. Anyone heard of anything like this or have any suggestions?