The VRayOverrideMtl is a utility material provided with the V-Ray renderer. It allows a surface to look different depending on whether it is seen through reflections, refractions, or GI.
With this material you can get a fine control over the color bleeding, reflections, refractions, and shadows of the objects.
The example image by Linda Ferroni demonstrates the reflect material override option. Notice that the yellow bottle and brown pot are reflecting as entirely different materials in the mirror.
Base material – Specifies the material V-Ray will use while rendering the object.
GI – Specifies the material V-Ray will use while calculating the GI solution.
Reflect mtl – This is the material V-Ray will use to render the object with, when the object is seen in reflections. For more information, see Using the Reflect material example below.
Refract mtl – This is the material V-Ray will use to render the object with, when the object is seen in refractions. For more information, see Using the Refract material example below.
Shadow mtl – This is the material that will be used to render shadows cast from the object.
