Hi,

I've made a patch to remove that ugly black rectangle from ns_ring_bell,
when visible-bell is 't.
The patch makes Emacs behave like the X version, inverting the colors of the
top and bottom lines, and bounces the Dock icon once if Emacs is not the
frontmost app (which can be extended to when visible-bell is 'nil, if
desired (just hoist it outside the if).

There is one difference in behaviour to the X version. When we have
horizontally-split frames, the scrollbars between frames also get inverted.
If we want to invert all the scrollbars, we just need to change the CGRect
calculations to not take the scrollbar into account.

Patch made against revision 99416.

Regards,

  Filipe