Fading Objects does not work (Unity 5)

Hello,

Im trying to fade in an GameObject. I read several methods, but none works as intended. There is no transition between invisible and fully visible. Im using the Unity 5 Standard shader specular setup (Renderer mode is set to "Fade"), which works best so far. There is no performance issue here.

                             alpha += alphaStep * Time.deltaTime;
                             currentC = Color.Lerp(fadeInStart, fadeInEnd, alpha);
                             Renderer[] r = GetComponentsInChildren<Renderer>();
                             foreach(Renderer skin in r){
                                 skin.material.SetColor("_Color", currentC);
                             }

EDIT One thing I have to mention: The mesh starts with Cutout Rendering Mode and changes to Fade via Script and back later.