Crannell, C. W. (1964). Code learning and color. The Journal of Psychology, 58, 295-299.

Upon exposure of associated pictures of the decorative sticker variety, four groups of college students learned to produce letters of the alphabet or numerals or simple words. Two methods of learning (whole and part) and two types of pictures (in full color and in black-and-white) were assigned at random to Ss so as to make up the four groups. Neither method nore code type was found to affect the number of trials taken in original learning nor the amount of recall after three weeks without intervening practice. The materials tended to be unusually easy to learn and to retain, and it is suggested that when this is true, little is to be gained by the use of color in the stimulus pattern.