JQuery code meaning in the post

what does this query means :

var bgColors = {
even: '#fbf9f7', odd: '#FFF'
};
$(document).ready(function () {
$("table.row_style tr:even").addClass("white");
$("table.row_style tr:odd").addClass("cream");
});

Is it changing the alternate row background color
OR
Is it changing the font color in the alternate rows?