Unity - Animated alpha coroutine

private IEnumerator AnimateRevealing()
{
  renderer.enabled = true;
  var color = renderer.material.color;
  for(var time = 0; time < duration; time += Time.deltaTime)
  {
    color.a = time / duration;
    renderer.material.color = color;
    yield return null;
  }
  color.a = 1;
  renderer.material.color = color;
}