From what I have been able to dig up, a request was made by 15th Army Group at the beginning of November 1943 for the replacement of the Light Mud/Black scheme as soon as possible. A colour similar to Olive Drab was requested. Orders were issued by HQ 8th Army in January 1944, stating that Olive Drab would not become available until early spring and that until then a uniform dark green or dark brown was to be used where available. This applied to Commonwealth AFV as well (both these documents are attached).
New Zealand Divisional Cavalry Staghounds were repainted in April 1944, and I'm pretty sure from photos that the colours weren't Light Mud/Black (page 338):
http://www.nzetc.org/tm/scholarly/tei-WH2DiCa-c21.html
New Zealand tanks (18th Battalion) were repainted "Dark Green and Brown" in April 1944 (page 442) :
http://www.nzetc.org/tm/scholarly/tei-WH2-18Ba-c30.html