Hi,
Try to add the following code snippet to the Custom CSS area in Theme Settings to fix this issue.
.wpb-js-composer .vc_tta.vc_general.vc_tta-style-classic.vc_tta-tabs .vc_tta-tab>a {
color:rgba(255,255,255,0.8)!important;
}
.wpb-js-composer .vc_tta.vc_general.vc_tta-style-classic.vc_tta-tabs .vc_tta-tab.vc_active>a {
color:white!important;
}
.wpb-js-composer .vc_tta.vc_general.vc_tta-style-classic.vc_tta-tabs-position-bottom .vc_tta-tabs-container:after, .wpb-js-composer .vc_tta.vc_general.vc_tta-style-classic.vc_tta-tabs-position-top .vc_tta-tabs-container:after {
background: -webkit-gradient(linear,left top,right top,from(rgba(26,26,26,0)),to(#1a1a1a))!important;
background: linear-gradient(to right,rgba(26,26,26,0) 0,#1a1a1a 100%)!important;
}
Regards