WW2 Rank Backing Colours

Gentlemen,

Can anyone help me out here please? I'm trying to establish when officers wore the colour backing behind their rank badges (pips and crowns) on Battledress.

ACI 1118 of 1940 lists the colours to be worn, and later amendments like the Recce Corps green (ACI 420 of 1941) etc, were also made. I can't find the RADC (green) as yet though!

Some examples:

RAC - yellow. RA - red. RE - blue. R. Sigs - blue. Infantry - scarlet.
RASC - yellow. Air Defence Corps - green. RAPC - yellow. Int Corps- green.

My question is: when did officers wear these colours behind their rank badges? What I mean is, were the standard khaki type the default working dress / battle order type and were the coloured backings worn at HQ level, on best order / parade ground dress, etc, or, as has been suggested...vice versa for battlefield identification?

Help?

Ken