Hi Budgie
40 was the universal number for a divisional headquarters, or headquarters of divisional arms and services -
Black for Div HQ and odds and ends like the defence and employment platoon
Red/Blue horizontally divided for HQ artillery
Blue for HQ engineers
White/Blue horizontally divided for Signals, numbers in red
Red/blue/red in vertical strips for HQ div supply and
blue/yellow/red in horizontal strips for HQ EME.
All with white numerals except Sigs
For 1 Div I don't think HQ RAA and HQ RAE exist anymore, possibly none of the others either except Div HQ and probably 1 Comd Spt Regt uses the old Sigs plate being that it was based on 1 Div Sig Regt anyway.
I don't know if the Army still uses the coloured signs now.
Cheers, Keith