在更新面板上淡化背景颜色

I have a radajaxpanel that is populated with the selected item from a combobox on another update panel. Currently the radajaxpanel is the same background color as the rest of the page. What I'd like to do, is based on it being populated with data, change it's background color to a muted red.I have a radajaxpanel that is populated with th