One of my favorite lithops species. I really love the leaf top patterns. Leaf color really seems to vary. My L. otzeniana tend to be more reddish brown, rather than the gray color of yours. I've seen some with very greenish patterns which are quite nice. You really have a great collection of plants Alain. You should make a few trips to the States and give talks to local C&S societies. If you ever do, start with our society in Washington, D.C. :)
Reddish brown sounds nice. I have never given a talk or visited U.S. Seen it from Canada. I think S Africa/Namibia would come first for a trip.