<i>Shakudo</i> is one of the traditional Japanese alloys which is colored by <i>nikomi-chakushoku</i>, a traditional Japanese coloring method. <i>Shakudo</i> is a copper alloy containing basically 1 ~ 5 % weight gold. It is famous for its black surface, but this color does not appear before the alloy is treated by <i>nikomi-chakushoku</i>. The authors previously reported that the colored layer of <i>shakudo</i> consisted mainly of cuprite (Cu₂O). In this paper, the micromorphology of the colored layer was observed with a scanning electron microscope. The colored layer was found to be an aggregate of fine particles of cuprite; it was flexible and adherent. The distribution of copper, oxygen, and gold in the colored layer was detected with Auger electron spectroscopy. These results were compared with the data of the colored layer of pure copper. Analysis with a transmission electron microscope suggested that fine gold particles in the colored layer of <i>shakudo</i> influenced the purplish black color or <i>shakudo</i>.