That's a good point that you bring up. I would say no, not from sun or dusting. I have seen others (mostly cockerels) with the diluted red/brown coloring as well. Just trying to figure out what it is and if it's something I want to play with.
I will add that I have hatched full black mottled from these birds (I have a black hen carrying the mottled gene and must assume the dad does too). This is the first with blue of this kind though. I also believe I have gotten mille fleur in this pen, but did not keep the chick to grow it out to see the final color. I may have to just do just test hatching and see what else crops up. In addition, I've seen buff colored birds crop up, but I don't think I have anything that should produce buff in there. Would that be an indication of dun being present?