Recognition of signal colors has been studied by statistics of use of names of red, yellow, green, blue, and difficult, over a wide range of illuminance. Results have been compared with those obtained by other authors. The absence of “white” and inclusion of “difficult” in the permissible responses appear to be responsible for difficulties in the blue and yellow recognitions.
S. R. DAS, "Recognition of Signal Colors by a Different Set of Color Names," J. Opt. Soc. Am. 56, 789-790 (1966)