Copy-paste from IRC:

the taskbar icon is awful as someone who is colour-blind
cannot tell the difference between talking and not whatsoever
it's easy to tell in mumble itself due to the white background, the "waves" next to the person are obvious
I think I'd rather it be the actual mumble icon when not talking
as a "person" while idle doesn't represent what kind of program it is
then have the talking guy when talking
that will make the difference pretty obvious