The client provided me with the green paper. It's a special stash he has. On my first pass, I messed up the drawing but he'd only sent me one sheet of it. I told him about it and asked if he could send another sheet of green paper, but he was out. I searched paper stores in New York, where you can find just about any sort of paper, but could not find an exact match for this--it's acid-free, too.
He finally got some more paper and sent it to me, along with a back-up sheet in case I had another accident. As you may already have supposed, he has a collection of the Green Lantern Corps, all on this green paper.