This is the 'pearl' of a stingray skin. The contrasting color is not natural and is done with dye. If dyed all one color the raised dots nearer to the pearl tend to take less dye and thus tend to be a bit lighter. Somewhere along the way it became popular to extentuate this effect with the shape you see here. Personally I despise this effect. Though I very much like stingray (Shagreen).