It's possible for an olive egger to have brown spotting. Brown eggers are used in creating olive eggers so not unusual to have an array of spot patterns. The following website has lots of varied olive egg spotting & even has a breeding chart showing how the olive eggers are created. I found it interesting.Those are gorgeous. I loved the speckles so much. My favorite though has to be to be the random oddly “printed” eggs like something went awry in the paint boothThat egg is not dirty at all its just how it came out. Typically this chicken would lay a finely speckled Olive egg but clearly something went haywire.
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https://silverhomestead.com/breeding-speckled-olive-eggers/