A Micro-Electro-Mechanical System (MEMS) based Fabry-Perot array may be used as a spectral filter to light sensing array, such as a CCD or CMOS photodetector. Applying different voltages to the electrodes of individual Fabry-Perot cells within the array allows a gradient in the Fabry-Perot air gap across the Fabry-Perot array. In this manner the MEMS Fabry-Perot array serves as a spectral filter of light passing through the Fabry-Perot array to the photodetector array. Embodiments of the disclosed sensor, used with LEDs that emit light outside the photosensitivity range of a photoreceptor belt, may be used to measure spectral information from toned patches placed upon a photoreceptor belt within a marking system. Other embodiments of the disclosed sensor, used with LEDs that emit light of any wavelength, may be used to measure spectral information from toned patches placed by a marking system upon a non-photosensitive output substrate, such as an intermediate belt or paper.