Haha, I love the one of Joker jumping over Batman.
I think it might be the way they printed it and the fabric used. I'm thinking they might have used a white fabric as a base, but the patterns on the shirt are so tiny and condensed, it might have bled through slightly to what little bit the base fabric actually shows through. I'm not a fabric printing expert, so I'm not sure if that's possible, but right now I'm inclined to think that.
The square pattern I think is just an optical illusion of sorts. They all look the same size to me, but where the fabric folds away from the camera, they look smaller.