Where to change the color of Submenus (IE issue)

Hi, on IE, the Submenu on the Hero Template is white (See Pick).
I already know that the background of the submenu has a color that does not exist:

#site-header .menu-wrapper .primary-nav.home_menu ul.menu li ul.sub-menu li a {background: #ffffff45;}
A color can only have 6 characters, IE is choosing to use the first 6, which is #ffffff or white.

Question: Where can i change that? I cannot find it under Customizer. In the Customizer, it is white… See pic
pls Advise
txs