I've never seen exactly that, kind of looks like he rubbed up against paint, but have had some color change following molt in some of my birds. I've had random feathers come in completely or mostly white, and then come back colored the next molt. I've always assumed it's from less than pure genetic lines, causing it. I've one bird (an EE) that was soft, creamy, yellow/white her first year and has gotten increasingly dark, going buff or tan in more places every year after molt. If you are feeding a balanced diet, and you are not seeing any other symptoms or health problems I would not worry too much. If you were showing or breeding for standard it would be a concern. Maybe someone else will have seen what you have.
I definitely would look at diet. Lots of things can effect feathers, not enough protein, missing vital vitamins, minerals, amino acids, even lack of sunlight or not enough sleep can have an impact. Since he's a house bird, any or all of those things might be in play. I would put him on a balanced flock raiser feed (he doesn't need the extra calcium in layer feed), keep treats to 10% of his diet, try to get him outside for some daylight every day that it's possible, and try to have his sleep hours as close to real sunup/sundown as you can, as they would be if he was outside. The feathers that are already there will be that way until they are replaced, but you have lots of time to make sure the next set is better. And hopefully get him more healthy over all. As said above, it's always a good idea to check over for mites/lice whenever there is a feather question. If it progresses and gets worse, then mites would be suspected.
