Use product attribute drag-and-drop order (or term_order) to order colors in a Color facet

add_filter( 'facetwp_facet_orderby', function( $orderby, $facet ) {
  
  if ( 'my_color_facet_name' == $facet['name'] ) { // Change 'my_color_facet_name' to the name of your facet. 
    
    $term_ids = get_terms( [
      'taxonomy' => 'pa_color', // Change 'pa_color' to the name of the attribute used in the Color facet's data source setting..
      'term_order' => true,
      'fields' => 'ids',
    ] );

    if ( ! empty( $term_ids ) && ! is_wp_error( $term_ids ) ) {
      $term_ids = implode( ',', $term_ids );
      $orderby = "FIELD(f.term_id, $term_ids)";
    }

  }
  return $orderby;
}, 10, 2 );