Our ground plane isn't very interesting right now, but we can use Materials to breathe a little life into the level. Materials control how GameObjects are rendered in the scene, which is determined by the material's shader. Think of Shaders as being responsible for combining lighting and texture data into a representation of how the material looks.
Each GameObject starts with a default Material and Shader (pictured here from the Inspector), setting its color to a standard white:
To change an object's color, we need to create a material and drag it to the object that we want to modify. Remember, everything is an object in Unity—materials are no different. Materials can be reused on as many GameObjects as needed, but any change to a Material will also carry through to any objects the material is attached to. If we had several enemy objects in the scene with a material that set them all to red, and we changed that base material color to blue, all our enemies...