zinc phosphate on rally center caps?

Heres my dilemma two caps are covered in the texture and one is half covered but the last one has almost none left.It appears that the texture was put on and the whole thing was chromed.Doesnt look like any color was added to any of these.The two with the most texture are darker but looks like they are dirty which is hard to clean out,in the pics the derker ones are the ones with not much texture.Maybe these pics will help.