Using different materials on each instance of an object with a mirror modifier

Question

Is it possible to have each instance of an object with a mirror modifier using different material? An example would be a door modeled only on one half, but where each side would be in a different color:

Or is applying the modifier permanently the price to pay in order to be able to do this?

Answer 1

You will have to go around the mirror modifier and create 2 copies of the door each with different material, but with the same mesh they share between each other:

1. Get rid of the mirror modifier.

2. For each material slot set it to be linked to Object:

   

3. Make an instance of the door with Alt+D. This will duplicate the object, but link the same mesh between them. More on this can be found here:

   What is a Duplivert, or a Dupliframe, internally?

4. Scale one object in the axis you want to -1 to mirror. Arrange them accordingly.

5. Assign different materials to the material slot(s).