In this work, we proposed a full-color reflector using three stacked red (R), green (G), and blue (B) reflection gratings which are combined with the tunable 90° twisted nematic liquid crystals (TNLCs). The color reflector based on guided-mode resonance (GMR) gratings reflects strongly at the resonance wavelength. The optical reflectivity of GMR gratings can then be controlled by using 90° TNLCs to change the polarization of incident light. The optical characteristics and the chromaticity of the designed reflectors were evaluated by simulation. An individual RGB chip with/without LC was demonstrated experimentally. The fabricated GMR reflector for red exhibits a high TE/TM polarization ratio of >10:1 and 80% optical reflectivity at resonant wavelength, while the GMR reflector for blue only allows 60% optical reflectivity and a degraded polarization ratio of 3:1 mainly due to high optical absorption of silicon. Nevertheless, the silicon-based GMR reflector enables a wide reflection bandwidth, so a full-color reflector can be realized by vertically stacking RGB tunable reflectors. The proposed full-color reflector therefore exhibits a wide-gamut color space with low driving voltage of <3 V, showing its promise for use in energy-saving reflective information systems.