How can I highlight admin comments?

Basically what I want is to have all comments posted by admins with different background color than the rest, so they’re easily distinguishable.

I wasn’t able to find any plugin that would do this though, and hacking it into the theme doesn’t look very clean.

Any suggestions?

By default WordPress already adds user/admin/post author specific CSS to comments with the following three elements.

#byuser
#comment-author-admin
.bypostauthor

So you can just add something like #comment-author-admin {background-color;blue;} to your stylesheet.