I have a colour chip card for RAAF aircraft and vehicle colours, but there is no mention of a RAF Blue-Grey or just Blue-Grey, so it possibly dates from after the period that RAF Blue-Grey was discontinued. There is no date on the card.
The text states: "The Camouflage Coverings are applied by spray after thinning with equal volumes of enamel thinners, and two coats are necessary to ensure complete coverage and achieve the desired result. Aircraft/Vehicle markings are applied manually by brush, and the material is used straight from the can. These coverings form the finishing coat of a system utilising Red Oxide Base and Base covering Aluminium which conforms to the intent given in RAAF specification K5."
Source:
Colour chart help