the stage occurring immediately after the deathly black stage or nigredo, and just prior to the pure white stage or albedo… the appearance of all the colours of the rainbow, which look like a peacock displaying its luminescent tail
Abraham provides the definitive technical account of the peacock’s tail as the chromatic transitional stage between nigredo and albedo in alchemical process, corroborated by Philalethes and Roger Bacon.
, A Dictionary of Alchemical Imagery, 1998thesis