Get back some colors in Finder's sidebar
You aren't alone in wanting the color back.  Unfortunately, it looks as if the Finder code actually shifts the hue from the fully-colored icon resources that are included (see the Go menu in Finder, which has the colored versions).  

According to a commenter on this MacThemes Forum thread, the developer documentation actually details how to shift the hue in the same way that Finder does; with the associated speculation that we'll see grey icons in every app that has a sidebar in the future.

Looks to me as if you can bite the bullet and use ColorfulSidebar (with SIMBL) or live with the grey.