[Sorry - have been away from PPRuNe for a few days, so am late replying!]
BRL - I've never seen it written anywhere, but I believe that the requirement is for the waistcoat to meet the requirements of EN471:1994, which I had always taken to define that the colour was fluorescent yellow. A quick Google advises me that the orange waistcoats also comply with EN471:1994, which surprises me; the average rail worker that I see in the EasyJet style waistcoat doesn't catch the eye anything like as well as the yellow waistcoats.
I have a 'mesh' style waistcoat to the same design (more comfortable / less smelly in summer!) as well as one of the standard style - one Jobsworth at Bournemouth once pointed out that the mesh was non-compliant with EN471 and that I should obtain one which was compliant!!
