Well as you may all be knowing after using Windows 7 for years, the taskbar buttons are all flat and the active (selected) window button doesn't really feel pressed or pushed. In fact it is slightly brighter and therefore it is hard to notice which is the active (foreground) window.
In the screenshot below, the window in the middle is the active window (3rd one):
This is a usability disaster because it's not easy to tell and you must figure it out before you can, for example, minimize the foreground window by clicking again on its taskbar button. Luckily, there is an Aero-based theme mod for Windows 7 that fixes this issue so the active (foreground) window button appears slightly darker and also looks like it is pressed or pushed.
Notice how in the screenshot below, the window in the middle is darker, appears to be pressed/pushed and therefore it is immediately clear regardless of the color of the taskbar which window is the active/selected one:
I am sharing the theme here but since it is a patched/third party themes based on Aero and because Microsoft allows only signed theme to be used officially, you must install some app first that allows you to use third party themes. I recommend UXStyle since it does in-memory patching. So first install UXStyle for Windows 7 from here:
http://uxstyle.com/And then download this theme, (copy it/extract files to C:\Windows\Resources\Themes) and double click Windows.theme file to apply it.
Before you apply the theme, make sure UxStyle is installed and stop and restart the "Unsigned Themes Service" from Services.msc.
Everything else about the Windows 7 Aero theme remains the same, only the look of the active window button on the taskbar is changed to fix the usability.
It is another step in enhancing Windows 7's taskbar usability. If you want to fix your Windows Taskbar, like Classic Shell fixes your Start Menu, check out
7+ Taskbar Tweaker.