use same color for label as in explore dropdown

public/sass/components/_group-heading.scss

@@ -1,5 +1,6 @@
 .picker-option-group {
   cursor: default;
+  color: $text-color-weak;
+  font-size: $font-size-sm;
   font-weight: $lead-font-weight;
-  color: $btn-primary-bg-hl;
 }