<?php

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'my_facet_name' == $params['facet_name'] ) { // change 'my_facet_name' to the name of your facet
        $params['facet_display_value'] = get_term_meta( $params['term_id'], 'color', true );
    }
    return $params;
}, 10, 2 );