I don't know what color eggs the BA lay, but dad's black cochin hen lays a lighter brown egg with white spots on it, kind of like the pores of the egg? So it could be the cochin.
I believe I had gotten them in March, so she'd be about 4 months old.
![idunno.gif](https://www.backyardchickens.com/img/smilies/idunno.gif)