When a Boolean object is generated, new surfaces are created. 

These surfaces are always in the same material as the surface from which they have been created. 

If red cuboids are punched out of a grey cuboid, for example, the outside surface of the generated object will be grey and its holes red. 

If the partial surfaces of the Boolean objects are to subsequently be given a different colour, this can be done by editing the operand objects in the property window or by pulling a material onto the operand object by drag and drop.

To do this, the operand object must, however, have been selected beforehand.

1. Subtraction of objects with different materials.                                                     2. Red cubes are subtracted from the grey cuboid.