The use of color as a coding device has been limited in some important applications because a practical maximum of only about 15 absolutely identifiable colors have been found experimentally. This investigation was undertaken to determine whether or not substantial improvement in color identification could be obtained as a result of extended practice. One subject practiced on Munsell color chips for about five months. Performance improved continuously, and at the end of the practice period the subject was able to identify 50 colors with almost perfect accuracy. However, errors increased markedly during three months of no practice immediately following the training period.
R. M. HANES and M. V. RHOADES, "Color Identification as a Function of Extended Practice," J. Opt. Soc. Am. 49, 1060-1064 (1959)