This has been around a while, but I have just started implementing it on sites. This detail adds a nice touch, further extending the color scheme and also makes text on dark backgrounds easier to read when highlighting. Highlight the text on this page, you will see it is black on green. The browser default would be gray on a light blue background, which is not easy to read. Below is the code I used:

::selection { background:#c3effd; color:#000;}
::-moz-selection { background:#c3effd; color:#000; /* Firefox */ }