This doesn't quite tell the full story as it misses out the 'Classic' leather type from the Sport Seats section. And doesn't really draw out the fact there are 2 types of Sport Seats, with and without bulge/codpiece at the front.
As best as I can tell the Nappa leather type is a rarity on Sports Seats and is usually mistaken for the more rugged Classic leather. The Nappa is the best type of leather and has a smoother grain. Nappa is standard on M Seats.
Both Nappa and Classic come without the codpiece and are always single colour.
Oregon and Chameleon come with the codpiece and can be either 2-colour or single colour. Those are my working assumptions but looking to confirm!
Also trying to find out what type of leather is on the bolsters of the Oregon and Chameleon seats.
Haven't got my head round non-Sport seats yet!
Will post back when I'm happy I know the full story. I've also emailed the guy who owns the onlyz3 web site.