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you could create your own "theme" by styling the code and pre tags, but that would only give you the background and font styling. To have individually colored code snippets you could use something like http://prismjs.com/.
Not sure, if that's what these people are using on their sites, but that would be an option to use.
 
Somehow my first thought was github.com. Or were you thinking something less intense and nerdy??
 
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