Dye composition and dyeing method

A dye composition comprising:

• a non-aqueous dye;
• and an ionic liquid wherein the non-aqueous dye is a polymethine dye comprising a cyanine dye, a merocyanine dye or an oxanol dye, and wherein the cyanine dye is represented by formula (I):
• wherein Za and Zb each independently represents an atomic group necessary to form a 5- or 6-membered nitrogen-containing heterocyclic ring;
• R1 and R2 each independently represents an alkyl group or an aryl group;
• L1, L2, L3, L4 and L5 each independently represents a substituted or unsubstituted methine group, provided that when there are substituents on L1 to L5, the substituents may be linked to each other to form a ring;
• j represents 0, 1 or 2;
• k represents 0 or 1;
• Xn− represents an n-valent anion;
• and n represents an integer of 1 or more.