Change “You are now logged out” text

This allows for the message to be overwritten specifically for the loggedout message while leaving all other messages alone. Here is more documentation on the filter.

add_filter( 'wp_login_errors', 'my_logout_message' );

function my_logout_message( $errors ){

    if ( isset( $errors->errors['loggedout'] ) ){
        $errors->errors['loggedout'][0] = 'This is the <strong style="color:red;">logged out</strong> message.';
    }

    return $errors;
}