Custom separator styles are only available in the Pro version, but you could also change separators with a CSS snippet. For example, a basic white line:
#adminmenumain #adminmenu li.wp-menu-separator {
height: auto;
}
#adminmenu li.wp-menu-separator .separator {
border: none;
background-color: #ffffff;
height: 2px;
}
You can add CSS to the WP admin with plugins like Add Admin CSS or Admin CSS MU.