Just cooked 4 racks yesterday. Mine also looked green, but only on the bottom.
I use a 3-2-1 method for smoking. 3 hours of smoke, then wrap tight them in foil with some fruit juice leaving room for steam and smoke another 2 hours... then open up for one hour and the meat will start to separate from the bone.
I usually use grape for smoking... and then use grape juice for the 2-hour steam. However, yesterday I used apple juice instead of grape... and mine turned yellow for the first time ever.
I can't guarantee that is what the problem was, but all signs point there.
Same process, same batch of meat as before... but different results with the apple juice.
Other than the color, they were still great!