Increment thresholds were determined for bichromatic mixtures of 660 and 520 nm (red + green), and 440 or 460 and 570 nm (blue + yellow). These measurements were made against a 1000-td white background that was surrounded by a larger, luminance matched annulus that appeared steady or flickered at 10 Hz. Targets were circular spots that subtended 60 and 15 min arc and had durations of 10 and 200 msec. All mixture thresholds with the steady surround were non-additive. The flickered surround gave rise to a periphery effect (PE), in the form of elevated mixture thresholds compared to those using the steady surround, for both red + green and blue + yellow mixtures when the 60 min arc, 10 msec spot was used. A PE was not consistently observed for the other three stimulus conditions. We propose the non-additive results indicate parvocellular (P-) pathway involvement in detection, which occurred under all stimulus conditions tested. Furthermore, that the PE were found when mixture stimuli were large, and brief indicates magnocellular (M-) pathway involvement in detection.