Marbled seems to be quite a recent mutation and there is no standard for it as yet so all marbled are classified as non standards. I don't think they are hybrids or else he would be disqualified so I think this is a recognised mutation. I would say he is actually in between a Normal and a pearl so perhaps there is some suppression of the pearl making him half in half
I think there are mottled in Campbells spuds mum which are also non standard I believe.