Just a follower putting in two cents... I haven't said anything for several weeks because I wasn't sure if you had already thought of it, but since you're asking, here you go:
You did pick Cheeto out of solids by his one white feather (which you never found again - so it probably faded out). You put him in a pen with a lot of permanent spotties (I think), and so most/all of the chicks ended up with fading spots of varying amounts ... Basically, I'm saying, fading spots could be another gene in addition to spots and no spots. And it seems to me that fading spots may be dominant over permanent spots, though the amounts of spots may switch around.
Just a suggestion.
I'm absolutely not an expert on this whatsoever, but hopefully I've helped you a bit.
You did pick Cheeto out of solids by his one white feather (which you never found again - so it probably faded out). You put him in a pen with a lot of permanent spotties (I think), and so most/all of the chicks ended up with fading spots of varying amounts ... Basically, I'm saying, fading spots could be another gene in addition to spots and no spots. And it seems to me that fading spots may be dominant over permanent spots, though the amounts of spots may switch around.
Just a suggestion.