Interesting little snippet from Motor Sport, talking about how BRG was chosen.

Starting with Olive Green " It’s unclear why the colour was chosen but some think it was to reflect the standard colour of many British-built industrial machines of the time. In 1903 the Gordon Bennett Trophy was to be run in the UK but with racing on public roads banned, the organisers switched it to Ireland (then still part of Great Britain). In honour of their hosts the olive green was changed to emerald green and British Racing Green was born. Whether the Irish origins of British Racing Green are fully appreciated by OneNation is unclear."

The One Nation reference is to the new political party who have chosen BRG as their party colour.