As a photographer I am really into Nike’s designs. They love dark gradients, and that really sells if for me, because Nike shoes are so colorful. The visuals that you will always see in Nike is that when they design they keep the same pallet. like lime green shoes, with a link bar with the same effect.
I agree with your comment about the dark gradients. Having these really strongly composed photos against a crisp, clean white background is very effective. The products become very visually appealing and interesting to look at. This is especially relevant when they are on a model and preforming what is intended to represent some kind of elite workout. These pictures sell themselves as every consumer looking at them wants to imagine they can look the same when they too buy the product.