I have seen 6/2 WG that has black and red wires (there is some in my house), but I have never seen it for sale myself. So, I don't know if it is even available anymore.
Actually, I believe that this design is newer rather than older. Correct me if I am wrong, but I believe that black and red is required for two-wire "Loomex" (Romex) over #10 in Canada. If that's really the case, it would make sense that cable manufacturers would standardize with one cable design, especially with today's copper prices. Of course, type SE cable has always been black/red and is very common in the US for higher-amperage 240 volt circuits. Besides, who has ever seen a 50 amp 120 volt circuit?
(No need for feedback from folks in New York City where there are 50 amp, 120 volt feeds to apartments in very old buildings. That's different)!