How to set the transparency of an object?

Hi guys. I'm making an android app using Unity and I need your help.

I want to change the transparency of an object. It has some children and each one has more children. Each component has a texture applied and I want to set the transparency of the higher level object. I'm already setting Transparent/Diffuse to the shader.

I made a recursive function to change the transparency of all children:

 void setColor(Transform go, float transparency)
     {
         Color c = new Color(go.renderer.material.color.r, go.renderer.material.color.g, go.renderer.material.color.b,transparency);
         foreach (Transform child in go)
         {
             child.renderer.material.color = new Color(c.r,c.g,c.b,c.a);
             setColor(child,transparency);
         }
     }

The call of the function is:

 setColor(getObject(gender,"Skin").transform,transparencyValue);

The access of the object is ok.

I want to maintain the texture I'm applying and just change the alpha of all children.

Why I can't change the transparency? Is it due to the fact that there's a texture applied and I'm changing the color? Is Transparency/Diffuse ok? I've tried to set Transparency/Cutoff/Diffuse and then change the cutoff but nothing happened.

Somebody help me, please. Thanks.