Nine color blind subjects were discovered in a survey of 140 Aymaras of Arica, Chile, using as screening test a portable Anomaloscope, Ishihara tables and Hardy‐Rand‐Ritter plates. Pseudosisochromatic test failed on detecting four anomalous trichromates. Seven color blind subjects revealed foreign ancestors. Also a different prevalence of defectives among subsamples was observed. Thus color blindness variability within the sample could be explained by gene flow. It is proposed to use anomaloscopes as a screening device in order to survey with accuracy color vision genes in human populations. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company