There is a problem with calling class attributes outside PHP classes. Could you please give me some advice?

Question

<?php

class Animal{

  public $name;

  public $color;

  public function __construct($color){

    $this->color=$color;

  }

  function write($name){

    echo $this->name=$name." Can write!";

  }

  function run($name){

    echo $this->name=$name." Can run!";

  }

}

$dog=new Animal("yellow");

$dog->write("Dog");

echo '<br/>';

$sheep=new Animal("white");

$sheep->run("Sheep");

echo '<br/>';

echo " sheep color is ".$sheep->$color;  //这行报错，该怎么调用$color这个属性？

 ?>

Answer 1

$sheep->color, do not need the $

in front of color

Answer 2

echo " sheep color is ".$sheep->color; //This line is written like this. If $ exists, color will become an undefined variable?