As an Edmontonian, I have never been very fond of the city flag, which is basically the coat of arms on a blue version of the Canadian flag. The green you are using apparently comes from the "grassy mount" on which the shield's supporters are standing. This minor detail doesn't, in my view, merit use as a main colour. Other than blue, the main colours on the shield are purple and gold, either of which would (I think) would work better than green. Whatever secondary colour is used, make sure there is sufficient contrast to be able to read the numbers. White or gold would be far better for this. Based on the arms, Edmonton's "official" colours are purple and gold (not used by any of its major sports teams). I never thought about using the gold, i'll make sure I update it before my next post What would you suggest for their sponsor?