Basic WordPress customizer setting.

wp-cl-customizer.php

<?php

namespace Passy;

add_action( 'customize_register', __NAMESPACE__ . '\\customize_register' );

function customize_register( WP_Customize_Manager $wp_customize ) {
	
	$wp_customize->add_panel( 'custom_login_settings',
		array(
			'priority'    => 10,
			'capability'  => 'manage_options',
			'title'       => __( 'Custom Login', 'custom-login' ),
			'description' => __( 'Style your wp-login.php page with ease.', 'custom-login' ),
		)
	);
	
	$wp_customize->add_section(
		'custom_login_form',
		array(
			'title' => __( 'Custom Login Form', 'custom-login',
				'panel'           => 'custom_login_settings', // WordPress 4.3
      			'capability'      => 'manage_options', // If different then the panel 'capability'
      			'priority'        => 10,
          )
				);

    $wp_customize->add_setting(
	    'form_background',
	    array(
		    'default'    => '',
		    'type'       => 'option', // this is a option not a theme mod AKA get_option()
		    'capability' => 'manage_options',
	    )
    );

    $wp_customize->add_control(
	    new WP_Customize_Color_Control(
		    $wp_customize,
		    'form_background',
		    array(
			    'label'    => __( 'Form Background Color', 'custom-login' ),
			    'section'  => 'custom_login_form',
			    'settings' => 'custom_login_settings["design"]',
		    )
	    )
    );
}