There is provided an aqueous solution containing (a) a preservative and (b) at least one azo compound represented by the following Formula (1) or a salt thereof, in which the content of (b) is 1% by mass to 25% by mass. (In Formula (1), G represents a nitrogen atom or —C(R2)═. R2 represents a hydrogen atom, a sulfo group, a carboxyl group, a substituted or unsubstituted carbamoyl group or a cyano group. X1, X2, X3, X4, X5, X6 and X7 each independently represents a hydrogen atom or a monovalent substituent. Y2, Y3 and Y4 each independently represents a hydrogen atom or a monovalent substituent. Y2, Y3 and Y4 may be bonded with each other to form a ring. All of Y2, Y3 and Y4 do not represent hydrogen atoms at the same time. M each independently represents a hydrogen atom or a monovalent countercation.)