Four stages [of the alchemical opus] are distinguished, characterized by the original colors mentioned in Heraclitus: melanosis (blackening), leukosis (whitening), xanthosis (yellowing), and iosis (reddening) … the xanthosis, otherwise called the citrinitas, gradually fell into disuse
Hillman establishes yellow bile’s alchemical correlate, citrinitas, as the omitted fourth stage of the opus whose loss reduces the quaternary symbolic system and forecloses a dimension of psychic transformation.
, Alchemical Psychology, 2010thesis