Decolour Remover is only able to remove artificial permanent colour pigments. It contains no hydrogen peroxide and is not capable of lightening natural hair pigments. If you have removed and observed your natural colour has not returned. Instead, the hair appears to be warm, ginger or copper; this is indicating the permanent colourants you had previously applied have lightened your natural hair colour. All permanent colourants need hydrogen peroxide to function. However, some brands of permanent colour use much stronger peroxide volumes in the developer than others. Even black and dark brown hair colourants can feature peroxide strengths capable of lightening away natural pigment, as the new pigment deposits. This lightening of natural pigment is often not noticed until the unwanted permanent colour removes, then the lightened base is exposed. Quite often warm, as the natural red and gold pigment has been revealed.
How to remedy
The key with unwanted warmth is to neutralise and counteract. So, use a product like Colour Restore Cool Ash or Lilac Grey to balance out the exposed warm tones within the hair, and wash only in a blue or purple shampoo. These haircare approaches will cool exposed warmth and produce a neutral base shade.