Sprite's Color Doesn't Change in Simulator

Hi,
I want to give hints to player when player press the button. When player press the button, button will change color of the sprite. I wrote the code and tested in “Game” tab and It worked. But When I use “Simulator” tab, sprite’s color doesn’t change. It is still white. I also tested it on Unity Remote and result didn’t change.

Here is the code I wrote. Thank you for replies.

public void GiveHint()
    {
        if (hintCount > 0)
        {
            // Get "List<GameObject> hints" lenght.
            int Lenght = hints.Count;
            // Create random number between 0 and Lenght variable to determine which hint(sprite) show up.
            int random = Random.Range(0, Lenght);

            // Change color of the sprite(hint).
            hints[random].GetComponent<SpriteRenderer>().color = Color.green;
            // Remove the sprite from the hints list.
            hints.RemoveAt(random);
            // Remaning hints.
            hintCount--;
        }
    }

I changed this code

hints[random].GetComponent<SpriteRenderer>().color = Color.green;

to this:

hints[random].GetComponent<SpriteRenderer>().material.color = Color.green;