Another option is to use the same tank for both sides, but paint them differently. If I remember correctly they exactly did that in the movie Patton. The Americans were driving in green colored Pershing tanks or M48s, the Germans were driving khaki colored Pershing or M48s. I am referring to when the two met in North Africa. I will take a look and see if I can find the scenes of the battle.
In the movie A bridge too far, there is a German tank crossing the bridge and it is supposed to be a Tiger, I guess. What kind of tank are they using in the movie and trying to make it look like a German tank? Is it a Comet?