Current menu item

Are you only trying to change the text colour on hover?

If you just want to change the text colour (not JUST on hover, but also just when the user is on that page).

/* This targets the current page's menu item */
.current-menu-item > a{
background-color:#123456;
color: white;
}

/* This targets other menu items when you hover over them */
.menu-item:hover > a{
background-color:#123456;
color: white;
}

If you need more specificity, then you can either add the .menu-item class, or whatever bootstrap class is being applied (.nav or .nav-bar usually)

So your first rule would be

.menu-item.current-menu-item > a{
background-color:#123456;
color: white;
}

This is just based on the picture, without seeing the actual markup, it’s hard to tell – but just inspect the element using your browser’s built in dev tools and you should be able to easily see what styles are being applied and with what specificity, then you simply craft your rule to be higher.