Abstract: A device for detecting differences in color of a material to be inspected, which device comprises a first light source emitting light of a first color and a second light source emitting light of a second color, an optical system adapted to project portions of the light emitted both by the first and the second light source onto first and second spaced apart measuring regions respectively, each measuring region being associated with means for measuring the amount of light reflected by the material. The device further comprises electronic switching means for alternately energizing the first and the second light source, means for transporting the material, means for controlling the intensity of the second light source in dependence upon the measured amount of reflected first light source light, and means for determining a difference in color from the measured amounts of reflection.