Check out the Water to Wine article on this site. It shows how acid-base indicator color changes are caused by changes in electron confinement. You'll find links on the bottom of the article to several relevant sites (some with Java applets that let you see how electron confinement affects color).
Author: Fred Senese firstname.lastname@example.org
Copyright © 1997-2010 by Fred Senese
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Last Revised 02/15/10.URL: http://antoine.frostburg.edu/chem/senese/101/quantum/faq/print-electron-confinement-and-color.shtml