Can you put a permanent red hair dye on top of a permanent brown hair dye?

I am a licensed Redken Certified Haircolorist. You should NEVER overlap permanent hair color. Permanent color has higher levels of ammonia which will dry and damage the hair. New hair (virgin hair) that has never been colored can be colored with permanent hair dye in order to cover gray or lighten. If ends are faded, a demi-permanent hair color should be used to refresh, brighten and add shine.