A front page article a while back mentioned that Apple had scrapped plans for an anodized black aluminum Macbook Pro because scratches showed up very noticeably because of the contrast between the coating and the underlying metal.
I think that Liquidmetal, which is a material that Apple has purchased exclusive rights to, can actually be colored all the way through. I'm pretty sure that we'll see more color options in their metal cases if/when they finally start using Liquidmetal in their products.
My dream iPad would be the thickness of an iPhone 4, with the back material looking like the stuff they made the lid of the Samsung Series 9 out of. Hell even make a stainless steel band all around the outside of it, and a glowing Apple Logo