I have noticed that there is an opacity rather than a total colour change on the main menu.
I have inserted the code below in the appearence section for custom css. The problem is that the sub-menu background on hover is still transparent. The slider loading bar on wite can be seen going by and through the opened sub-menu.
.menu li a {
color: #ffffff;
opacity: 1;
}
.menu li a:hover {
opacity: 0.5 !important;
}
.menu > li > ul > li > a:hover {
color: #ffffff;
background: #000000;
opacity: 1 !important;
}
It is not the opacity issue or transparency issue but the z index issue which you can resolve by adding the following CSS code in the Custom CSS option of your theme on the below path.
Admin Area -> Appearance -> Customize -> Shapely Options -> Other