This is a scrollwatcher example.

When the middle third of the "one" or "two" <li> elements scrolls into view, the <li> will change into a non-black color. When the middle third of the <li> scrolls out of view, the <li> will become black.

When the center of the "three" <li> element scrolls into view, the <li> will change to blue. When the center scrolls out of ivew, the <li> will become black.