I'm not sure about colours but start at
http://www.canplates.com/quebec.html
The plate shown as 1937-1943 appears brown (slight reddish tinge) on my monitor with white print. I have no idea if all plates for a given year were the same colour or if cars and commercials had different colours. the pictured plate seems to be white print on dark background which fits the above. Another site says that 1940 car plates were white on black.
A third site shows both car and truck plates for the same tears (but not 1940, oldest shown example is 1966) and the colours are the same in each case shown.
The linked site contains confirmation that the plate is commercial, not car, apparently F=frais.
As curiosity Quebec's 1944 plates were black lettereing on a light grey background on a masonite plate. Ontario for 1944 was a decal placed on the windshield to extend the 1943 plate.