<?php

public class Dog {

private $name;

private $color;

private $breed;

public function Dog($name, $color, $breed) {
   $this->name = $name;
   $this->color = $color;
   $this->breed = $breed;
}

public function getColor() {
   return $this->color;
}

public function test(Dog $dog) {
   $dog->color = 'Brown';
}

}

// some examples

$mydog = new Dog('Rover', 'Red', 'Labrador');

// prints out 'Red'
echo $mydog->getColor();

$anotherdog = new Dog('', '', '');

$anotherdog->test($mydog);

// prints out 'Brown'
echo $mydog->getColor();

?>