That white chick does not look like an ISA Brown male.
The leg color is a bit wrong. ISA Browns should have yellow legs, but those look a bit green.
The comb is definitely wrong. ISA Brown should have single combs, but this is not a single comb. I think it may be a weird version of a pea comb, but there's a chance it is a rose or walnut comb. Regardless of which one it is, it is definitely not single.
Given the comb and the leg color, and considering what kinds of chicks are most likely to have those traits, I think it may be an Easter Egger. Hatcheries seem to have many kinds of Easter Eggers lately, with many different feather colors and a variety of other traits. Female Easter Eggers typically lay eggs of some shade of blue or green, although a few lay shades of brown instead.
No signs of rooster yet … 6 weeks in …
I agree, no signs of a rooster yet.
I would watch for the comb to get red (male) or stay pale (female) over the next month or two. That type of comb is not going to stick up the way a single comb does, so comb color will tell you more than comb size on this bird.