Customize color with empty default

customize-empty-default-color.php

<?php

add_action( 'customize_register', 'my_customize_register' );

function my_customize_register( $wp_customize ) {

	$wp_customize->add_setting(
		'color_xyz',
		array(
			'default'              => '',
			'sanitize_callback'    => 'sanitize_hex_color_no_hash',
			'sanitize_js_callback' => 'maybe_hash_hex_color',
			'transport'            => 'postMessage',
		)
	);

	$wp_customize->add_control(
		new WP_Customize_Color_Control(
			$wp_customize,
			'color_xyz',
			array(
				'label'    => esc_html__( 'XYZ Color', 'textdomain' ),
				'section'  => 'colors',
			)
		)
	);
}