If its concrete paint it using concrete paint
Could be mildew still. May need a better power washer (more PSI). Or try spraying with mildewcide like JOMAX, and rinse. Should kill the mildew and get better over the coming weeks.
Try scrub brush with bleach
There is a product called "wet it & forget it" that is supposed to be good.
try sanding the areas that are discolored.