42 Commando RM flag

Does anyone know of the origins of 42 Commando's flag?
It is different to those of the other Royal Marines commando unit flags, with the yellow background and a red cross that has a white border.
When I served with 42 in the early 60s it was always flying alongside 3 Commando Brigade HQ flag outside the admin block , (known as the "bird cage") at RNAS Sembawang.
45's flag, by contrast, was dark green with a red Fairbairn Sykes knife and the numbers 4 and 5 (also in red) on either side.
In more recent years, the flags on sale by multiple sources are of a more standardised format.
Any ideas would be welcomed.