Interesting, we went from Morocco to Mali through Western Sahara, Mauri, Senegal, Guinea Bissau, Guinee in Jan - May of this year.
The green labels for unleaded disapeared just south of Laayoune. They sold unleaded and also sold super in Laayoune which made me believe that unleaded would disappear in place of leaded (super). The guy assured me that there was no unleaded but only super in the desert.
We didn't see the green unleaded labels until Bamako. We had bikes with no cats so we didn't care but we are about to do the trip again in petrol 4x4s and I had the cats removed...perhaps I shouldn't have. I had read on the internet that leaded was supposed to be phased out but seeing as it's Africa, I just figured it hadn't. Some people had had problems with leaded fuel and their catalytic converters but that information might have been quite old.
I did speak to a man in western sahara that had been running his unmodified peugeot essence on super for a while and said that he had no problems.
If someone gets a definitive answer on this, I'd be interested.