To provide a first agent for oxidation hair dye in a constitution containing a carbonate in the first agent for oxidation hair dye, the first agent for oxidation hair dye being capable of improving stability of the dye, and a method for stabilizing a color tone of hair dyed by an oxidation hair dye composition. The present invention is concerned with a first agent for oxidation hair dye containing a carbonate, the first agent including (A) at least one selected from resorcin and its derivatives, and salts thereof, an upper limit of a compounding amount of the component (A) being 0.2% by mass or less, (B) at least one coupler selected from m-aminophenol, 5-amino-o-cresol, and ±； -naphthol, and (C) 0.01 to 0.45% by mass of at least one dye intermediate selected from p-phenylenediamine, toluene-2,5-diamine, p-aminophenol, N,N-bis(2-hydroxyethyl)-p-phenylenediamine, and derivatives thereof, and salts thereof, a mass ratio of a content of the component (B) to a content of the component (A) being 0.5 to 10.本發明提供一種在氧化染毛劑第一劑中含有碳酸鹽的構成中，能夠提升染料的穩定性的氧化染毛劑第一劑以及氧化染毛劑組成物的色調穩定化方法。本發明為含有碳酸鹽的氧化染毛劑第一劑，其中含有(A)成分、(B)成分以及(C)成分，該(A)成分是選自間苯二酚及其衍生物、以及它們的鹽中的至少一種，且(A)成分的調配量的上限為0.2質量%以下，該(B)成分是選自間氨基苯酚、5-氨基鄰甲酚、以及α-萘酚中的至少一種調色劑，該(C)成分是選自對苯二胺、甲苯-2,5-二胺、對氨基苯酚、N,N-雙(2-羥乙基)對苯二胺及它們的衍生物、以及它們的鹽中的至少一種染料中間體，且含量為0.01質量%~0.45質量%，並且該(B)成分的含量相對於該(A)成分的含量的質量比為0.5~10。
