Holy cow, I wrote a book!
I hadn't even noticed this until somebody pointed it out:
When you hover your mouse over a button in the Windows 7 taskbar
which corresponds to a running application,
the taskbar button lights up in a color that matches the
colors in the icon itself.
(And even more subtly, the lighting effect is centered on the mouse.)
This feature even has a name:
Some people ask how it's done.
It's really nothing special.
The code just looks for the predominant color in the icon.
(And, since visual designers are sticklers for this sort of thing,
black, white, and shades of gray are not considered "colors"
for the purpose of this calculation.)