How to Change the Dock Indicator Lights Color in Mac OS X only for an app that I'm using right know?
The Dock indicator light does not differ between which app is in the foreground.

As a workaround, you could install a third party item called HyperDock (for EUR 6.95 as of this writing) to show you the content of the window when hovering over the icon with the mouse (similar to how Windows' Aero Desktop does).