http://www.constructionenquirer.com/2016/05/11/coloured-hard-hats-to-make-sites-safer/

May be a little complicated until we get used to it?

My current employer has used this system for many years, black hats for supervisors, white for operatives, orange for slinger/signallers and yellow for traffic marshals.  Has worked quite well across most projects particularly in locations where there are still individuals who refuse to wear particular colours due to religious/football followings e.g. N. Ireland & Scotland where blue & green hats can cause problems.  As long as all those coming onto site are aware of the requirements there are seldom any issues.  The black hats can make it very easy to identify who to approach on site.  The danger will always be when each trade or client wants to change, amend or add to what already works well.  It would be good to see a standardisation of HI-Viz clothing across the industry with one colour and full length sleeves a common standard, IMHO.