At the moment a build shows a green ball even if all test cases are failed.
It would be nice to mark the job "red" if at least one test case fails.

I would prefer the following:
1. Testlink Plugin option to configurable reaction in case of testcase failure.
Cancel testplan execution if a testcase failed or continue with next testcase.
2. If one or more testcases are failed (result = not ok) the build should be marked as failed (red ball?).
3. If execution of the build (testcase) shows an error (slave missing, batch file not found...) the build shoud be marked as broken or something like that.
In that case the ball should be filled with a colour except the used (green, red, yellow, blue)

Job Colours:

running - yellow
passed - blue/green
failed - red
broken - to be defined

Or we mark broken jobs as red and the failed once with a different colour.