Fader.cs

public float TargetAlpha 
{
// TODO: validate on Set (0.f .. 1.f)
get; set;
};

void Update() {
    Fade();
}

void Fade()
{
  Color c = renderer.material.color;
  if (!Mathf.Approximately(c.a, targetAlpha))
  {
    // Scaling up or down
    // TODO: Move to 'rate' variable?
    var alphaAdjust = targetAlpha < c.a ? -.1f : .1f;
    
    // Frame rate independence
    alphaAdjust *= Time.deltaTime;
    
    // TODO: Check potential bug with shifting c.a past target alpha and oscilating, verify if not an issue depending on FPS?
    
    c.a += alphaAdjust;
    renderer.material.color = c;
  }
}