tablesorter odd/even not working

Is there anything that I need to do to get the odd/even color to display? Isn't it automated?

I have it in the css:

table.tablesorter .even {
    background-color: #E1F7E6;
    border: none;
}
table.tablesorter .odd {
    background-color: #FFF;
    border: none;
}