1. The spectral-response bandwidth and peak sensitivity of the responses of color-opponent retinal ganglion cells of the macaque monkey were examined in conditions of neutral adaptation. Color-opponent cells showed specific "signatures" in plots of response bandwidth versus wavelength of the peak sensitivity that allow for an acceptable estimate of the cone types whose signals mediate cell responses. 2. Averaged spectral bandwidths of color-opponent ganglion cells were compared with published data from color-selective neurons of subsequent levels of the geniculocortical pathway, including the extrastriate area termed V4. No significant differences were found between color-selective cells of the retina, dorsal lateral geniculate body, striate cortex, and V4. 3. The spectral location of the peak sensitivity of responses of the various types of color-opponent ganglion cells showed a relatively broad distribution, loosely clustering at some spectral loci. Comparison of such distribution with that of recently reported V4 cells response indicates that a remarkable scarcity of "blue/yellow" opponent responses in such reports. 4. In association with more recent electrophysiological studies of V4 cells, the results do not support current claims of a color specialization of this extrastriate area, and suggest lack of significant spectral tuning of the retinal output in, so far known, higher visual centers having color-selective cells.