How Can I fade An Object?
Assuming you mean fade from transparent. You could adjust the vertex colors or use a shader.
For example using the Transparent/Diffuse shader you can adjust material.color property from code.
If by ‘fade’ you mean ‘make an object transparent’, you can give an object a new material, make that material’s shader “Transparent/Diffuse” and then set the Alpha value of the material color to the transparecy that you want.
If you mean to turn an object gradually invisible, you could use a material with a semitransparent shader (like Transparent/Diffuse) and modify its Main Color alpha value (renderer.material.color.a) towards 0 to make it vanish, or towards 1 to make it solid again - but be aware that semitransparent shaders may become a nightmare if there are other semitransparent objects or billboards (like far trees or particle effects) overlapping: these shaders don’t update the Z buffer, what may make them to appear in the wrong order (a closer object is rendered behind a farther one).
A partial solution is to use an opaque material (Diffuse shader, for instace) most of time, and switch to a Transparent one (like Transparent/Diffuse) when you need to do the trick - this avoids problems when the object moves, since it can pass in front or behind billboards and semitransparent objects without causing this annoying effect.