Create another “Display Site Title and Tagline” checkbox, “Header Text Color” setting and control

If the setting and controls are added exactly as they appear in class-wp-customize-manager.php the JQuery script in wp-admin/custom-header.php will toggle the header text color control properly. The theme_supports line must be commented out or removed as it is “used to hide a setting if the theme lacks support for a specific feature”.^[1]

add_action( 'customize_register', function ( $wp_customize ) {

    $wp_customize->add_setting( 'header_textcolor', array(
        // 'theme_supports' => array( 'custom-header', 'header-text' ),
        'default'        => get_theme_support( 'custom-header', 'default-text-color' ),

        'sanitize_callback'    => array( $wp_customize, '_sanitize_header_textcolor' ),
        'sanitize_js_callback' => 'maybe_hash_hex_color',
    ) );

    $wp_customize->add_control( 'display_header_text', array(
        'settings' => 'header_textcolor',
        'label'    => __( 'Display Site Title and Tagline' ),
        'section'  => 'title_tagline',
        'type'     => 'checkbox',
        'priority' => 40,
    ) );

    $wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'header_textcolor', array(
        'label'   => __( 'Header Text Color' ),
        'section' => 'colors',
    ) ) );
});