Visual hints to better spot the currently active window?
There isn't a lot that's easily customizable about color schemes on OS X. One suggestion is that if you're using the Graphite color scheme, switch to the Blue color scheme. In earlier versions of OS X,there used to be quite a bit of difference between them, and many developers went with the more subdued Graphite scheme, but by Lion, one of the only surviving differences is the traffic-light dots in the upper left corner of a window. In the graphite color scheme, they're all grey, but in the "blue" scheme, they're colored when the window is the active one.