Your new birds look like Welsummers. That's a fun breed and lays dark brown eggs.
If you got them while still in the chick down I can see how the mistake was made.
The chicks aren't that much different in color in the down stage if the Speckled Sussex were
based on the e+ ( wildtype) allele and not the eb(Brown) allele. In the USA e+ is
common for Speckled Sussex, I think.
The difference in down is that the eb chick has a brown helmet. The e+ chick has
an arrow of brown down ascending up the nape of its neck and crossing the top of
the skull. So if your Speckled Sussex chicks were e+ they would have looked very
much like the Welsummer chicks which are e+.
An allele is the genetic canvas upon which the colors are painted.
speckled Sussex chicks in down (e+):
Welsummer chicks in down (e+):
3rd, 4th and 5th pics are Welsummer chick.
Here is a pic of an eb chick exhibiting the "brown helmet". Actually this chick was e+/eb. One copy of each allele. I hatched him. He feathered out like an e+ rooster. But his chick down is definitely eb. He was a Marans. the White chick is (I think) what is called a "White Pearl" but don't quote me on that.
Edited by 3riverschick - 2/9/16 at 6:52pm