It's been bugging me for a long time, but... ...why do we have to know the colours of the letters and the background of the various hazard signs? Chances are that the bloke writing the initial label will have white paper and whatever colour marker pen comes to hand. Besides, the hazard is written in big letters. Roadsigns convey their meaning by shape and colour - prohibitive, mandatory, hazard, restriction, information, etc but CBRN signs rely on the small print - date, type, measurement and so on - so identifying the colour from a distance doesn't help very much. Was the idea developed by someone with too much time on their hands and everyone else has just accepted it?