Edit superfish.css, and modify the colors in the following (comments added):

.sf-menu a, .sf-menu a:visited  {
    /* text color */
    color:                      #13a;
}
.sf-menu li {
    /* box color for top-level menu items */
    background:         #BDD2FF;
}
.sf-menu li li {
    /* box color for second-level menu items */
    background:         #AABDE6;
}
.sf-menu li li li {
    /* box color for third-level menu items */
    background:         #9AAEDB;
}
.sf-menu li:hover, .sf-menu li.sfHover,
.sf-menu a:focus, .sf-menu a:hover, .sf-menu a:active {
    /* box color for menu items when the mouse hovers over them */
    background:         #CFDEFF;
    outline:            0;
}