3 digit Hex values are also viable. It's a short-hand for double digits. Saves 3 bytes!
em { color: #69b } /* #rgb */
em { color: #6699bb } /* #rrggbb */
See:
http://www.w3.org/TR/CSS2/syndata.html#color-units
http://www.w3.org/TR/css3-color/#numerical