One purpose of the present invention is to provide a brown to dark brown dye that has excellent acid resistance and/or salt tolerance and that is capable of minimizing the occurrence of precipitates, spotting, uneven coloring, and the like even when used under conditions in which the pH is low or salt concentration is high. As a result of adding 1 wt% of citric acid to a brown to dark brown dye solution in which a brown to dark brown dye is dissolved in water such that a color valency E10%(500nm) = 0.1, a brown to dark brown dye having characteristics such as the ability to maintain a state in which 60% or more of said brown to dark brown dye is dissolved has excellent acid resistance and/or salt tolerance and is capable of minimizing the occurrence of precipitates, spotting, uneven coloring, and the like even when used under conditions in which the pH is low or salt concentration is high.
