add_filter( 'manage_edit-colourmedia_columns', 'colourmedia_columns' ) ; // init function
function colourmedia_columns( $columns ) {

	$columns = array(
		'cb' => '<input type="checkbox" />',
		'thumbnail' => __( 'Thumbnail' ),
		'category' => __( 'Category' ),
		'title' => __( 'Name' ),
		'city' => __( 'City' ),
		'featured' => __( 'Featured' ),
		
	);

	return $columns;
}