PURPOSE: To prevent the title product from discoloration without impairing the functions of the fibrous material when said product is used in composite, by treating a transition metal-containing fiber with a metallic ion-blocking agent to block the transition metals in said fiber.

CONSTITUTION: A fiber either surface-plated with a transition metal such as copper, cobalt, nickel, chromium, silver or aluminum or containing an oxide or sulfide of the above transition metal, or a fiber containing said fiber (e.g., through blending, combining, twisting, weaving), and a dyed product therefrom are treated with a metallic ion-blocking agent such as ethylenediaminetetraacetic acid to block the transition metals in said fiber followed by washing.