I was really stuck with to change the accordian each item header color, i was trying with

accordion.getHeaderAt(0).setStyle("backgroundColor","red");
accordion.getHeaderAt(1).setStyle("backgroundColor","green");

Thanks to Peter deHaan for the post ‘Customizing the Accordion header in Flex 3′.

See the example below for the Customizing the Accordion each item header background color in Flex 3