A slot waveguide utilized as a color-selecting element. The slot waveguide includes a first layer of plasmon supporting material, the first layer being optically opaque and having an input slit extending through the first layer; a second layer of plasmon supporting material facing the first layer and separated from the first layer by a first distance in a first direction, the second layer being optically opaque and having an output slit extending through the second layer and separated from the input slit by a second distance extending along a second direction differing from first direction; a dielectric layer interposed between the first layer and the second layer, the dielectric layer having a real or complex refractive index; and a power source electrically coupled to the first layer and the second layer to apply an electrical signal for modulation of the real or complex refractive index of the dielectric layer.