The idea behind switching to Olive Drab with no disruptive patterning was to avoid having to repaint the flood of US -sourced vehicles arriving in Britain for use by the British and Canadian armys.
The original wording of ACI 533 specifies the change in basic colour from SCC No.2 Brown to SCC No.15 Olive Drab.  This was a British colour, which was apparently of a 'greener' shade than US Army Olive Drab.  However, archival evidence seems to point to the Canadian Army using American-sourced paint, as currently, there has been no referrences found to the use of SCC No.15.

Section 21  Camouflage

2 (a) ‘A’ veh: One colour only will be used which may be any of the following:
      SCC Number 1A (dark brown)
      SCC Number 7 (dark green)
      Olive Drab (dark green)
 
 

HQ 4th Canadian Armoured Brigade
War Diary
28 October 1944

 A party headed by the SL, Capt.W.D.A.DOLAN, made inroads on the generousity of the US Army.  A visit produced much needed Browning MG spare parts and Olive Drab paint.  It is hoped that their gift will not detract from our allies war effort.

An M14 halftrack from ‘K’ section, No.3 Company, Royal Canadian Corps of Signals, attached to the 5th Infantry Brigade, 3rd Canadian Infantry Division, summer, 1944.  This is an example of the US-Sourced vehicles that would likely not have been repainted from it's original OD.
 
 
 
 
 

A dispatch rider astride an early model Harley-Davidson WLC leads a convoy of 3-tonners bringing food to the starving Dutch population under the white truce flag, April 1945.  The leading F60L and the M/C bear the markings of 3rd Medium Regiment  RCA.  The trucks and the M/C are both likely finished in Olive Drab.