Replace the color codes (#fffff and #000000) and add the css in theme options – design – custom css or  in child theme style.css (if you installed it from theme pack).

Header mobile menu

.mobile_header {
  background-color: #ffffff;
}

.mobile_header i {
    color: #000000;
}

Mobile Menu item

.snap-drawer {
    background-color: #282D33;
}

.user_mobile_menu_list, .mobilex-menu {
    background-color: #e38130;
}

.user_mobile_menu_list li a, .mobilex-menu li a {
    color: #FFFFFF;
}

.user_mobile_menu_list li, .mobilex-menu li {
    border-bottom: 1px solid #555;
}