The css for the subheader is found in app/style/scss/elements/_subheader.scss

.psub--dark {
  background-color: $templateColor;
 .breadcrumb {
   li {
    color: $lightgrey;
    a {
     color:$lightgrey;
    }
   }
 }
}
.psub--light {
  background-color: $subheader;
 .breadcrumb {
   li {
    color: rgba(0,0,0,.5);
    a {
    color: rgba(0,0,0,.8);
    }
   }
 }
}

You can choose for the HTML markup if the style of the subheader is dark or light.