Nick's has--or used to have--Mexcel leather available, but I'm pretty sure they also offer Horween's CXL now. I got a pair in Natural and I've seen pics of guys getting pairs in olive CXL, and no mention of it being a different, non-Horween version of CXL.
There are different grades (is it the right word?) of CXL--e.g. the one used by Wolverine and the one used by Viberg--but I wouldn't know what grade Nick's uses. Is it better than, say, White's? Beats me.