Just a thought, the unusual markings could be extra dark night camoflage markings. They get that when they are sleeping or relaxed while the light is dim (simulating dusk). They will also do that if they have no place to hide. The markings should fade at feeding time (may take a week or two) or when he is active. Getting some livebearer tank mates will put him at ease and his markings should fade to closer to normal mono colors. Get him some light colored mollies or platties so he feels like he is back at home with his other brothers and sisters. When he no longer needs his security blanket, he will snack on them.