I can tell you that after a year, the lighter hues will show more dirt than the darker ones. I'm actually replacing my light gray cover with dark gray because of how dirty my light gray one looks. My wife's green (first gen, not the new, brighter green) Smart Cover also looks very dingy now.
I bought a cream/white leather cover while trying out an iPad 2 briefly. I'm anal about my stuff and thought it would be workable.
Small coffee stains mysteriously appeared while at my boyfriends (the same day he'd been poking at it with dirty hands to tease me.)
It was only a week or so old and had nasty brown spots, albeit tiny ones.

I soaped up the entire leather surface with dishwashing soap which removed most of the marks, but I really shouldn't have procrastinated with a pre-emptive polish with Meltonian cream polish. Polish would really help repeal stains, I am sure.
The red was my other choice (to go with a white iPad,) and I sort of wish I'd gotten it instead.
But here is the big reason I am posting:
The leather covers can easily be dyed a darker colour if too soiled.
Leather dye can be found online or at cobblers, and it works great in my experience. I figured if the white became a problem then I'd just make it a unique shade. Burgundy, perhaps?
My new iPad arrives tomorrow, so I am trying to decide tonight whether to try the polish or to dye it now while the leather is most suited to it.

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JeffMorse,
That looks so much nicer!
Does it feel sticky from the oiling?
I oiled a tan Brooks [bicycle] saddle, and it promptly turned very dark, but it took a while to really absorb. I'd expect you can't saturate the smart cover enough for a great change without stickiness?
I think I have seen a product or two for creating the look you seek. Check that out if you aren't pleased with the oil?