Pretty hard to tell parentage unless there is a distinct dominant feature to follow.
Knowing that....
Since the hatchery told you it is an EE, and we'll trust their word, Ameraucana or Araucana should be in the background, preferably one of the parents.
Since it has a pea comb, and a bit of muffing, Ameraucana (or EE mix) was one parent, we'll assume they are a better quality hatchery and actually used an Ameraucana, which would be a smart thing to do if they were intending to pass along blue/green EE color eggs.
You can probably eliminate Cochin as those heavy feathered legs usually pass some down to the offspring. Same with Marans IF French style with leg feathering, although mine seem to have a 50/50 whether or not leg feathers passed down. (We'll come back to BCM later).
You can eliminate Dominque as it does not have a walnut comb. Both pea (from Ameraucana) and rose (Dominque) are dominant, and express together to make walnut. It has a clean looking pea comb, so Dominque is not likely in the background.
Probably not Brahma as that likely would have created leg feathers as those too are fairly heavy in the leg feathering which usually passes down.
So that leaves the Welsummer and Barnevelder and Buff Orp or a Marans American style (without feathered legs or they dropped off in first generation).
Since it is dark legged, I'm thinking the Black Copper Marans as Welsummer and Barnevelder have yellow legs, and Orpington white, BUT leg coloring is very tricky. I've had yellow Barnevelder roo over Cal Grey yellow/black wash hen produce chicks with slate grey legs....so let's look at the feather pattern.
Now it is a red partridge with heavy black lacing/patterning. BCM usually gives all black chicks as the black is pretty dominant. My Barnevelder roo (black body with brown wings, back, considered double laced) will produce red with black lacing over a reddish or partridge hen. The chick also looks a bit like a Barnevelder chick.
So my best guess would be the Barnevelder was used over an Ameraucana or EE, hopefully Ameraucana, which comes in 8 standard colors, a number of which would allow black lacing with red expression. The Buff Orpington is a possiblity too, but I think the legs and overall appearance are too dark, and there is no hint of Orpington in the body...but that is a possibility. Welsummer is a distinct possibility, but it usually throws a chipmunk wild type unless there is a dark color on the other parent, totally possible.
And, I think you may have a rooster. That coloring is very blocky looking, typical of a rooster. Hens will have regular, even color patterning. The comb is still pale, but that may be 3 clear pea rows, which also indicate rooster. Wait and watch. Hopefully the pattern will even out and the comb stay pale....otherwise, you've got a boy.
My thoughts
LofMc (who is breeding Barnevelder rooster over Splash Marans, Cream Legbar, Black Isbar, Red Sex Link, Cal Grey, to produce a colorful egg basket and colorful plummage).
