After watching Mr. Greene's oil video I took note of the brand of paint he uses, Lafranc & Bourgeois, and found a web site for them. On the palette page they list their sap green as "Permanent Sap Green". So, my assumption is that he's using a mixed sap green too.
Administrator's note: try this site as one of many offering L & B paint. http://www.allartsupplies.com/item.asp?cid=172 My browser couln't translate the L & B site from French.