The wheels, wheel nuts, tow hitch, bumpers, manufacturers badges, knobbly bits, ancilleries, hub drive flange nuts, etc should all the the same colour as the vehicle. The only exception to this is that in divided rim wheels the retaining nuts should be painted red and nothing else. This is repeatedly laid down in, Equipment Regulations, Joint Service Road Transport Regulations, AESPs. There is no requirement to paint anything else red or white even.
But some units will embellish some vehicles with all sorts of silly bits painted. I remember being taken round a camp by the chief vehicle inspector & asked him why about a third of the vehicles on camp have these unauthorised bits of paintwork. He just shook his head in despair & sighed that he can't stop them doing it whenever his back is turned!