Dominant hen or roo? (Meet Butter)

[NatJ]

She was a Rural King straight-run bin chick, sold as a "rainbow egger" (which I believe is just a "we don't know what these are" mixed breed label). I think Rural King gets their chicks from Hoover's Hatchery.

https://hoovershatchery.com/rainbow
Hoovers does have a specific group of chickens they call "Rainbow."
The photo shows chickens in a variety of colors, some of them quite similar to yours.

Those Rainbows are not a pure breed, but they have been selected and bred to have certain traits (such as body size & shape, egg laying ability.) So it is not just a case of "don't know what these are."

I am 99% certain she is a barred rock/buff orpington mix because she is SO fluffy, has the golden feathers, and has some barring on her outer feathers, and all her inner gray feathers are softly barred as well. She is also very friendly and gentle around people, she'd probably live in the house with us if we let her There could totally be a third breed in there as well.

Lots of other mixes could have those traits as well.

A direct cross of Barred Rock and Buff Orpington will generally produce chickens with a lot more black than your bird has.
Example photos in this thread:
https://www.backyardchickens.com/th...rred-rock-buff-orp-cross.112415/#post-1309918