Provided are a one-part hair dye composition containing (A) a combination of 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid, (B) either one of (b1) ascorbic acid or salt thereof or (b2) sulfurous acid or salt thereof, and (C) an alkali agent and having a pH of from 8 to 11 and a method of selecting the kind of Component (B), thereby controlling a hair color upon dyeing the hair.
