Multi-component package units (kits-of-parts), ready-to-use agents for reductive decolorizing of dyed keratinous fibers, and methods for reductive decolorizing of dyed keratinous fibers are provided herein. In an embodiment, a multi-component package unit (kit-of-parts) for reductive decolorizing of keratin fibers includes, separately packaged, a first container (A) and a second container (B). The first container (A) includes a cosmetic agent (a) and the second container (B) includes a cosmetic agent (b). Agent (a) in the first container (A) includes (a1) thiourea. Agent (b) in container (B) includes (b1) one or multiple oxidizing agents chosen from the group of hydrogen peroxide, potassium persulfate, sodium persulfate and/or ammonium persulfate.
