Horizon graphs divide a plot into bands that are collapsed into a smaller space and distinguished by color. In the below plot, dark blue represents the largest positive change, medium blue a moderate positive change, light blue a small positive change, and red is divided the same way for negative changes.

Stock change over the last year for six large tech companies. Graph produced in IDL.

A more detailed explanation is available at Panopticon site. In particular, follow the sequence of diagrams halfway down the right side of the page and their captions.

Found via Stephen Few’s blog.