You can achieve it by adding the following CSS code in the Custom CSS code option of your theme on the below path.

Admin Area -> Appearance -> Theme Settings -> Custom Code -> CSS Code

#page-container .sh-nav li.menu-item-type-custom a {
 background-color: #000;
 padding: 0 10px;
 color: #fff;
 margin: 30px 0;
 border: 1px solid #DF343C;
}

#page-container .sh-sticky-header-active:not(.sh-header-4):not(.sh-header-5):not(.sh-header-6) .sh-nav > li.menu-item-type-custom > a{
 margin: 15px 0;
}

You can change the color value in the above code to whatever you want to use by referring the following pages.

http://www.w3schools.com/html/html_colors.asp
http://www.w3schools.com/html/html_colorvalues.asp
http://www.w3schools.com/tags/ref_colorpicker.asp