How to add change alpha possibility?

[PoN]

I would like to add possibility to change an alpha of material by slider in UIPanel. I have my own shader for 3d object , i'd like to change slider position of alpha on UIPanel that changes alpha of material on 3d objects. What i should to add in the shader ?

[ArenMook]

Color c = renderer.material.color;
c.a = slider.value;
renderer.material.color = c;