To obtain a water-based ink composition which does not blot and strike through on plain paper recording, enables high quality (highly precise, high chroma) records having excellent water resistance, excellent light resistance, excellent scratch resistance and high color concentration, and contains a self- dispersing type yellow organic pigment.

A coloring agent is characterized by comprising a self-dispersing type yellow organic pigment which is obtained by subjecting an acid treatment for enabling the dispersing of a non-self dispersing type yellow organic pigment in water in the absence of a dispersing agent to the non-self dispersing type yellow organic pigment and has ΔE1/ΔE2 ratio of ≤10 in a fading resistance test, wherein ΔE1 is a color difference (a color difference before the radiation of light and after the radiation of light for 24 hr), and ΔE2 is a color difference of the untreated non-self dispersing type yellow organic pigment.