David i use that css
/* Set Background of navigation bar */
.sticky-enabled .main-navigation.is_stuck {
background-color: #000000;
}
/* Set menu item colors */
.sticky-enabled .main-navigation.is_stuck .main-nav ul li>a {
color: #ffffff;
background-color: #000;
}
/* Set meni item current and hover color */
.sticky-enabled .main-navigation.is_stuck .main-nav ul li:hover>a,
.sticky-enabled .main-navigation.is_stuck .main-nav ul li[class*=”current-menu-“]>a {
color: #000000;
background-color: #ffffff;
}
But on mobile mine header is only white.