I have a 2011 with black interior. Don't know if it will be the same on the newer model, but I was a little disappointed when I received mine. The front part of the seats are black and a portion of the back of the seat; however, a lot of the back is covered in the beige color. Did not realize that a black cargo cover was available when I ordered mine, and as such I've got the beige looking one. You are correct the sides of the cargo area are the beige color, and I'm happy with the lighter colored cover. I'm in Florida, so it is a little better for me from a heat perspective.
You will be happy, I'm sure, with whichever you choose.