Howtogeek posted a guide about customizing the Windows 7 Taskbar icons for any application

Would you like to change out the icons on your taskbar with a beautiful set of icons that all go together?  Here?s how you can change out the random candy-colored icons for a stylish icon set of your choice.

As you use Windows 7 and keep more programs pinned to your taskbar, you may start noticing that your icons clash with each other.  From bright colored icons to more modern icons with text, seldom do your app icons truly go together.

So, instead of dealing with clashing colors and designs, let?s create new taskbar icons.  You technically can change icons directly from the taskbar.  Simply right-click on the icon in the taskbar or click and drag up to open the jumplist, then right-click on the program icon near the bottom of the jumplist and select Properties to change the icon. Unfortunately, though, the taskbar icons did not update immediately when changed this way, and sometimes didn?t change even after rebooting.

  How to Customize Your Windows 7 Taskbar Icons for Any App