Hi,

try this code.

HTML

Place custom class in your dropdown menu (I have used .dropdown-yourColor)

<!--Dropdown custom-->
<div class="dropdown">
<!--Trigger-->
<buttonclass="btn btn-primary dropdown-toggle"type="button"id="dropdownMenu1"data-toggle="dropdown"aria-haspopup="true"aria-expanded="false">Dropdown primary</button>
<!--Menu-->
<divclass="dropdown-menu dropdown-yourColor">
<aclass="dropdown-item"href="#">Action</a>
<aclass="dropdown-item"href="#">Another action</a>
<aclass="dropdown-item"href="#">Something else here</a>
<aclass="dropdown-item"href="#">Something else here</a>
</div>
</div>
<!--/Dropdown custom-->

CSS

Add to the custom class your color

<style>
.dropdown .dropdown-menu.dropdown-yourColor .dropdown-item:hover {
background-color: red!important;
}
</style>

Unfortunately, in your CSS code you have to use !important to overwrite mdb style.