It came up in a meeting between FBHVC and DVLA that black and silver could be used on all tax exempt vehicles, but seems that one part of DVLA don't talk to another and so as you say confusion reigns!
link here to the TRR forum
http://www.tr-register.co.uk/forums/index.php?/topic/53366-classic-number-plates/
Last edited by Malcolm T; 01/11/15 12:50 AM.