The routine gSetMaterialColour() sets the current material colour for the front and back faces of facets. Both values may be indices into the GINO colour table or 24-bit RGB true colour values returned from the function gTrueCol().
The material colour is multiplied by the current material table lighting coefficients (as set by gSetMaterialIndex()) to calculate the actual material settings of either face.
Setting the facet material properties using gSetFacetMaterialProps() overrides any values set by this routine and gSetMaterialIndex().