Don't worry about discoloration at all. There's no "paint", it's real anodized metal. The darker color comes from an etching process, that's the actual surface of the device.
I seem to be cursed with oily wrists, I have to clean the space around my trackpad once a week or so… but it's no worse than the Space Grey or Silver models.
Dust around the speaker grills is maybe a little more visible. I've come to hate those faux holes (they're not real except for a dime-sized space at the bottom, just for looks).
I put it in a bag that had a steel zipper inside once and thought "I should be careful about this, that could scratch," and there was indeed a visible scratch as soon as I took it out >_<
but basically it's gorgeous and such a nice change, just get one.