Analysis of information sources in references of the Wikipedia article "Ninjutsu" in English language version.
Goshiki-mai: These dyed rice grains were used to create discreet trails that could be followed either by the original dropper or by sharp-eyed comrades
DH Publishing is Tokyo's #1 publisher of Japanese pop culture books for the English speaking world.
Based on the combination of colors they dropped, or the number of grains, the Ninja could make over 100 different codes.