First, I know knights were not the only people to wear armour, but how clean was armour kept when on campaign? Did soldiers try to keep it shiny? Could you see your face in it or have the sun reflect off it to blind opponents? I recall reading of a charge of knights blinding foes with the sun glinting on visors, but I have no idea how literal that was, or simply was emphasising the perceived splendour of them charging the enemy.
A follow-up question, was it anything as shiny and artificial-looking as this?
In ffoulkes, The Armourer and His Craft, he discusses armour and helmets that are covered in velvet, not a loose cover but glued to the metal. So while shiny was technically possible, it may not have been as fashionable as colours. Mirrors of the day were polished steel, certainly.