We present extinction spectra of sodiumnitroprusside exhibiting holographic light scattering after irradiation with coherent light. A characteristic extinction band appearing in the vicinity of the wavelength of the pump beam was discovered as well as an increase of the extinction coefficient over the whole spectral range. Those features are proven to originate from diffraction of the probe beam from parasitic holograms and can be explained within the frame of a simple Ewald-construction.