Extensive measurements were made for detecting luminance and red- green flashes in the center of a bright yellow field. Thresholds, plotted in L and M-cone contrast coordinates, indicate that chromatic flashes are more visible than luminance flashes even at very small size (2' diameter). Over a wide range of flash diameters and durations the chromatic flashes are detected with considerably higher efficiency (in units of cone contrast energy) than the most detectable luminance stimuli (small drifting gratings). The higher gain of the chromatic mechanisms has important physiological implications and is potentially useful in display technology. Detailed studies with luminance and chromatic stimuli suggest that the chromatic mechanisms have a constant spectral tuning, even for spots as small as 2': the chromatic response is determined by a constant, equally weighted difference of L and M cone contrast. A suprathreshold luminance flash (a pedestal) facilitates detection of a coincident chromatic flash. Earlier studies suggested that the facilitation will grow strongly when the stimuli were decreased in size. In contrast, we find that facilitation is constant (2-3x) for stimuli from 2' to 2 deg diameter.