How can I add transparent color option in my color setting?

I have created font color settings at customizer but it does not include transparent color, How can I add transparent option also.

enter code here 

class site_font_color { public static function register ( $ wp_customize ) {

    $  wp_customize->add_setting('site_emakers_fontcolor', array(         'default' => 'No'     ));      $  wp_customize->add_control(new WP_Customize_Control($  wp_customize, 'site_emakers_fontcolor-control', array(         'label' => 'Display the Site Font Color?',         'section' => 'colors',         'settings' => 'site_emakers_fontcolor',         'type' => 'select',         'choices' => array('No'=> 'No', 'Yes' => 'Yes')     )));        $  wp_customize->add_setting( 'site_emakers_fontcolor',         array(             'default'    => '#000000',             'type'       => 'theme_mod',             'capability' => 'edit_theme_options',             'transport'  => 'refresh',             'priority'   => 120,             'sanitize_callback'  => 'esc_attr',         )     );      $  wp_customize->add_control( new WP_Customize_Color_Control(         $  wp_customize,         'mytheme_site_emakers_fontcolor',         array(             'label'      => __( 'Site Font Color', 'customtheme' ),             'settings'   => 'site_emakers_fontcolor',             'priority'   => 10,             'section'    => 'colors',         )     ) );  }   public static function site_output() {     ?>      <style type="text/css">          <?php self::generate_css('.site *, :not(.btn-secondary, .btn)',  'color', 'site_emakers_fontcolor'); ?>     </style>      <?php }   public static function generate_css( $  selector, $  style, $  mod_name, $  prefix='', $  postfix='', $  echo=true ) {     $  return = '';     $  mod = get_theme_mod($  mod_name);     if ( ! empty( $  mod ) ) {         $  return = sprintf('%s { %s:%s; }',             $  selector,             $  style,             $  prefix.$  mod.$  postfix         );         if ( $  echo ) {             echo $  return;         }     }     return $  return; } 

}

add_action( ‘customize_register’ , array( ‘site_font_color’ , ‘register’ ) );

add_action( ‘wp_head’ , array( ‘site_font_color’ , ‘site_output’ ) );