add_action( 'cmb2_admin_init', 'yourprefix_register_comment_metabox' );
/**
 * Hook in and register a metabox for the admin comment edit page.
 */
function yourprefix_register_comment_metabox() {

	/**
	 * Sample metabox to demonstrate each field type included
	 */
	$cmb = new_cmb2_box( array(
		'id'           => 'yourprefix_comment_metabox',
		'title'        => 'Test Metabox',
		'object_types' => array( 'comment' ),
	) );

	$cmb->add_field( array(
		'name' => 'Test Text Small',
		'desc' => 'field description (optional)',
		'id'   => 'yourprefix_comment_textsmall',
		'type' => 'text_small',
		'column' => array(
			'position' => 2,
			'name' => 'CMB2 Custom Column',
		),
	) );

	$cmb->add_field( array(
		'name'    => 'Test Color Picker',
		'desc'    => 'field description (optional)',
		'id'      => 'yourprefix_comment_colorpicker',
		'type'    => 'colorpicker',
		'default' => '#ffffff',
		'column' => array(
			'position' => 2,
		),

	) );
}