Two years ago I bought 6 Isa Brown Pullets from Tractor Supply. They turned out to be black with red tipped feathers on their necks. looking more like Marans.I kept three of them and bought a rooster that is a crossbreed. This year I decided to set up my incubator and hatch some eggs. I get three different sizes and three different colors of brown eggs from these three hens, My first hatch yielded three black chicks with light underside and seven yellow with brown and white striped backs. Could the difference in chicks be coming from the rooster?
From your description, your hens are black sex links, not ISA browns. Since sex links are themselves cross breed birds, mixing them with a mixed breed rooster will easily give you chicks that are all over the place, color wise.
