I get the reasons for the standardization, and the (usability) reasons for the selection of the colours. For a lot of wikis, they'll be (mostly) irrelevant because of the degree of customization, either at the wiki-wide level, or on an individual use-case level; a lot of people won't even notice. I'm agnostic on the issue of colour palette, generally speaking, although that might be because I know how to get around it if I really want to.
On the other hand, those are pretty boring (bordering on awful) colours. Yeah, I know...they're chosen for usability. But they're also the same colours I'm seeing just about everywhere else on the web (although in slightly different contexts). I'm not invested at all in whatever standard colours are chosen, but I'm not persuaded that making Wikipedia look like a lot of other websites is necessarily a positive thing. It's like all the web designers are using the same textbooks. And #ac6600 is not a colour I really want to see on my screen; ask any parent to think back to those first six months, and they'll explain...
Risker/Anne