QProgressBar busy on macintosh style

I've been trying all day to make a busy indicator with the QProgressBar just to discover that it works with the app style "windows" but not with the app style "macintosh"

Is it a bug or am i doing something wrong?

EDIT: so apparently it's working with the macintosh style as well, the only problem is that it's a full dark grey bar with a very slightly brighter grey moving on it.
Is it possible to change the colors of the progressbar to make it more clear that there is an execution running?