1. A computer-implemented method comprising: rendering on a display device a time-varying multi-color signal comprising a plurality of different color signals that are separated in phase from each other; during the rendering, capturing a plurality of images of a target that is illuminated by the rendered multi-color signal, the plurality of images representing a plurality of frames; tagging the frames with respective color values of the multi-color rendered signal at the time respective images corresponding to the frames were captured; applying a band pass filter temporally to the images to generate a plurality of filtered images; extracting a filtered response signal from the filtered images; generating a frame-level temporal correlation measure based on, at least, a frame-level temporal correlation between respective tagged color values and respective dominant color values of the filtered response signal; calculating across the plurality of frames, for each pixel location, a pixel-level temporal correlation score from temporal correlation between respective color values of pixels at that pixel location in respective frames and respective color values of the multi-color rendered signal at the time respective images corresponding to the frames were captured; generating a pixel-level temporal correlation measure based on, at least, the plurality of the pixel-level temporal correlation scores; and accepting or rejecting the target based on, at least, the frame-level and pixel-level temporal correlation measures.