Scrollbar can be hard to see in Plastique widget style

Steps to reproduce / test case
With the Plastique widget style the movable part of a scrollbar can be very hard to see in dark color configurations. Take a look at the attached screenshot from konqueror for example.

It takes quite a close inspection to see where it begins and where it ends. Other styles do not have this problem.

An option to make the scrollbar colored like in Klearlooks or Polyester would be nice.