Not respecting if statement

I have this code that is supposed to fade out the rotating yellow cube. But once the alpha reaches 0, it continues one more time until the alpha reaches -0.200 and the cube becomes blue before disapearing.

    if (disapear)
    {
        if (rndr.material.color.a > 0.0f)
        {
            rndr.material.color -= new Color(0, 0, 0, 0.2f);
            Debug.Log(rndr.material.color);
        }
        else
        {
            gameObject.SetActive(false);
        }

    }

Screenshot

EDIT: There is no problem for the red finish line wich uses the same code.