That actually happens in silver aros and jars as well where there are some in a batch that are darker than other some a re lighter than other. As it age it will just look like any other adult balck aros. I used to have one back in 2007 but it got no barbels. It was the same color as yours too but when it age it turned to just a any other black aros, so I sold it cause it got no barbels.