We have tried to fix this in the past and it is really painful:
* Browsers style scrollbars themselves and make very subtle contextual
decisions. For example on a Mac, scroll bars hide/show dynamically and
automatically change colors based on the background they are above.
* Styling scrollbars can be done in CSS but it is awkward and you end up
with style bars that look out of place on some OS/browser combinations.
* Most importantly, if you style them by hand you disable the nice
auto-styling and auto-hiding some browsers do, so it ends up looking worse
for a lot of folks.
I would be open to some one exploring different options, but it would have
to address these points and be tested on all OS/browser combinations. The
other option is to begin implementing our own scrollbars (a huge amount of
work and difficult with accessibility)