Hi,
That’s the result of the menu bar having a background color when the menu is not displayed over the header image (when this background would get removed).
You can force-remove the background with CSS:
.burgermenu-active #site-header-main,
.burgermenu-active .site-header-bottom-fixed,
.burgermenu-active .site-header-bottom.header-fixed .site-header-bottom-fixed {
background: transparent;
}
.burgermenu-active .hamburger span {
background-color: #fff;
}
We’ll look into whether this should be the default theme behaviour.