A multi-component packaging unit (kit-of-parts) for the reductive bleaching of colored keratin fibers which contains, in separately manufactured form, (I) a first container (A) containing a cosmetic agent (a) and ( II) a second container (B) containing a cosmetic agent (b) and - the agent (a) of the container (A) containing (a1) one or more reducing agents selected from the group consisting of formamidine-sulfinic acid, sodium dithionite, zinc dithionite, potassium dithionite, hydroxymethanesulfinic acid, aminomethanesulfinic acid, cysteine, thiolactic acid, sulfanylacetic acid (thioglycolic acid) and / or ascorbic acid, and the agent (b) of the container (B) containing (b1) one or more oxidizing agents of the group comprising hydrogen peroxide, potassium persulfate, sodium persulfate and / or ammonium persulfate , and the ratio by weight of the total quantity of all the reducing agents (a1) contained in the agent (a) to the total amount of all the oxidizing agents (b1) contained in the agent (b) having a value of 50.0 to 4.0 based on the weight total of agents (a) plus (b). Other objects of the present invention are a ready-to-use bleaching agent and a reductive bleaching process of keratin fibers stained with the multicomponent packaging unit. Unité d'emballage à plusieurs composants (kit-of-parts) destinée à la décoloration réductrice de fibres de kératine colorées qui contient, sous forme confectionnée séparément, (I) un premier récipient (A) contenant un agent cosmétique (a) et (II) un deuxième récipient (B) contenant un agent cosmétique (b) et - l'agent (a) du récipient (A) contenant (a1) un ou plusieurs agents réducteurs choisis dans le groupe constitué par l'acide formamidine-sulfinique, le dithionite de sodium, le dithionite de zinc, le dithionite de potassium, l'acide hydroxyméthane-sulfinique, l'acide aminométhane-sulfinique , la cystéine, l'acide thiolactique, l'acide sulfanylacétique (acide thioglycolique) et/ou l'aci
