Chocolate back and colors that were discontinued. Upgraded Floyd Gotoh(I believe this is available on all new Axis'). To my knowledge,no sound difference, but I don't own a regular Axis.
They are the same guitar except for the finish method (hand rubbed vs sprayed) and the brown back. The trem and nut used are the new style that EBMM is using on all Axis guitars these days. It does look like the tributes may have all got "premium" quilt tops as well...