Gasoline was sometimes dyed for marketing purposes, especially back when it was sold from pumps that had glass cylinders or sight glasses where the product was visible to the consumer. It was kind of a sales gimmick. Sunoco Blue comes to mind.
From what I've heard from others, Green Gasoline was a low (sub-regular?) grade of gasoline. I've heard of it having been sold by Sinclair, as well as by Deep Rock. I'm sure there may have been others. A good friend of mine has a Sinclair poster advertising Sinclair Green Gasoline for 11 cents a gallon - that's significantly cheaper than a lot of gasolines in the 20s and 30s.
I'd really love to see/have a scan of that document, and I'm sure others here would, too. What does it have to say about Green?
Wes