Reply To: How to Change Underline Color in Ajax Products Tab?

Hello,

Please add this code to the Theme Settings > Custom CSS > Global:

body .tabs-wd-63739a85824d2.tabs-design-default .products-tabs-title .tab-label:after, 
body .tabs-wd-63739a85824d2.tabs-design-alt .products-tabs-title .tab-label:after {
    background-color: red;
}

Best Regards