As a note, if a build goes red, then you build it, it blinks red in the main jenkins window view as it builds.

However, if the build completes, the icon never updates (back to blue for instance), so even if the job is done, the icon makes it look as if it is going forever (and/or forever broken).

In the attached file, imagine there is a red blinking dot on the right hand side (sorry screen capture skills got borked).