They changed it a while ago and now it's really hard to see where you are on a page by looking at the scrollbar. Seriously what are they thinking...
Is there a way to change its color/contrast?
As I know, Google chrome scroll-bar is not customize-able manually. however you can use themes or skins or plugins. two of the best plugins are Better Scrollbar and Rescroller. both of them lets you custom your scroll-bar.