Hi and welcome to HCM By your description it does sound possible that the accident may have initially caused the swelling and infected/cellulitis appearance. also there may have been a small bump or scratch or wound after the incident that could have led to cellulitis. Another possibility is that the spots have healed leaving a dark area or scar which could appear as a bruise. In any case, since the antibiotic course is almost complete and you have seen good results, the discolouration of bruising will take a few days to return to normal. If you see no change after a week , you can try a lightening agent like kojic acid to prevent dark scar if you desire. persisting swelling, new wounds , pain, fever or any such symptoms will require a revisit to your doctor. Hope this helps.