Gmail have rolled out themes/skinning, though they've not put a link to where you can change that yourself somewhere useful.
So if you'd like to change your Gmail theme, you can do so here:
https://mail.google.com/mail/?shva=1#settings/themes (More info via Lifehacker
here.)
I don't mind the new default theme, though what I *don't* like is the lower opacity font colour - just give me black text, dammit, I don't want the stinking grey! But I am trying to get used to it. And my greasemonkey
Better Gmail scripts alleviate that a bit. At least I think it will, they only made the change this morning so I haven't had a chance to look at Gmail at home on my extended Firefox.
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