void ColorizeButton()
{
if (selectedDefender)
{
Defender defender = selectedDefender.GetComponent <Defender>();
if (star.EnoughStarsFor(defender.price) == Stars.Status.ENOUGH_STARS)
{
GetComponent <SpriteRenderer> ().color = COLOR_ACTIVATED;
}
else
{
GetComponent <SpriteRenderer> ().color = COLOR_ACTIVATED_NOT_ENOUGH_STARS;
}
}
}