New "Carbon" in Fresh Step?

So, I ran to the grocery store to buy another tub of fresh step (I buy the giant 28 lb thing- so the last time I bought it was in January). On the tub it says "New and Improved Odor Control Carbon!" The litter is a different color, too. It used to be blue and white, now its blue, white, and dark grey.
What does carbon have to do with cat litter? Has anyone used it and thought it was better or worse?

I've got some I haven't used yet. I assume it's for smell control, but fresh step was already pretty good.