A hair colouring formulation/kit for generating tannin-iron complex based stable wash proof hair colour is provided, which is pH dependent. A method of colouring the hair is also provided comprising sequentially applying the pH dependent hair colouring ingredients selected from tannin source, ferrous ammonium sulphate and potassium carbonate as pH modifier, affecting the degree of dissociation of said ferrous ammonium sulphate and ionization of tannin thereby influencing the activity in water base to facilitate darker colour shades on hair free of any additional ingredients and any additional intermediate step of washing of hair while application of the selective ingredients.
