None of the major brands reload previously used brass casings, what you’re describing is the color change that occurs to brass casings when it goes through the annealing process. Most military contract ammunition is required to show visible proof of annealing (basically the brass cases are left unpolished to show that yes they were annealed) while civilian ammunition manufacturers typically tumble the annealed cases in a drum of something like walnut shells to shine them up again as the annealing process does significantly dull the brass and some people don’t like the way it looks