Aluminum wire insulation

[GG]

I have been installing aluminum wire for my services since copper theft is happening so often. I went to buy some 4/0 aluminum at the supply house and all they had was insulated black with a green stripe on its insulation. The guy behind the counter said I can use it for my phase conductors, but I didn't trust this info so I didn't buy it. What does the green stripe supposed to represent ?

 

[GG]

I'm guessing its to be used as a grounding conductor only but why mark an entire roll of 4/0 with a thin green stripe when we have green tape.