If there are to be special helmets then they should be for special occasions - I don't mind Schumacher's 299th GP special from last week. But, surely the colours on a helmet are the drivers' livery - it makes them recognisable.
Felipe lime green, Fernando light blue. Michael red, Nico yellow. Jenson blue, Lewis yellow. It works. Take a look at the iconic Senna images and say his "brand" wasn't helped by the recognisable yellow with those two stripes. It beggars belief that Vettel changes his so often.