Help with Billboard visibility

Unity Engine
1

I added a random plane into the scene and attached the following line of code to make it billboard or sprite behavior:

function Update()
{
    transform.rotation = Quaternion.LookRotation(Camera.main.transform.up,Vector3.up);
}

The only problem I got now is, that the billboard is always visible. See picture below: The billboard is actually attached to a cube which is behind the yellow wall. However I don’t want it to be visible by the camera in that case. How can I change that?

446043--15512--$Untitled-2.jpg

2

Hmm partly solved I guess: I put the texture shader to “GUI-Textshader” which obviously rendered it on front… Now I set it back to “Diffuse” and it works fine.

Still another thing is strange: I have used a bright red texture but now the color is darkred…How come that?

Edit: solved too; I just changed it to Self-Illuminated-Diffuse.