A polycarboxylic acid mixture comprising 80% by weight or more of 1,3,6-hexanetricarboxylic acid, wherein the polycarboxylic acid mixture has a psychometric lightness L-value of 98 or more, a psychometric chroma a-value of from -2.0 to 2.0 and a psychometric chroma b-value of from -2.0 to 3.0, and has a nitrogen content of 5,000 ppm by weight or less.