Pontius has it right. Our fleet also has a coloured collar on the AURAL WARN SPKRS cb.
I did a high speed aborted take-off a couple of years ago when an Air Data Computer failure sent my ASI off scale and the Altimeter spinning skywards.
The noise associated with the overspeed warning was deafening, and you cant even begin to think until you have got rid of that noise.
The collars came about after the Birgenair crash.