The official colour for Highways workers is changing from yellow to orange. This is because psychological research has shown that yellow is associated with an obstacle but orange is more associated with a human being, and if motorists identify the blob of colour they have registered as a human, they will be more careful. It is therefore part of the same coordinated approach to improving safety as the "let my mummy come home to me" signs.
I learnt this at the safety induction before doing some work on the M40 hard shoulder. Apparently it cost £2M to instigate the new colours for the first big contract on the new system, on the M1.
They should get their money back.