Many apps alternate default background and a shaded or highlight background to help the eye follow items horizontally in a list box. I cannot get any combination of CSS, divs, spans, and options to change the background color of a list box on an item-by-item basis.
Based on the description this sounds like you want CSS 3's "nth-child" pseudo-selector. See http://www.w3.org/TR/css3-selectors/#nth-child-pseudo for more information.
*** This bug has been marked as a duplicate of 6248 ***