I was just surprised with the revival because every other part seemed to have had any number of ethnicities play them. And it worked well, in part due to talent but also the timeless, modern take on a period-set piece. I forget now how long it took, but it was years before a black Roxie was cast.
A cursory scan of IBDB for Chicago cast replacements leads me to think Robyn Givens might have been the first African American to play Roxie in 2006 (in fairness, many of the replacements don't have listed dates). By that time there had been about half a dozen that had played Velma. By the way, the list of replacements in the Chicago revival runs longer than the King James Bible.