Composition for colouring fibres

A process for treating fibres, the process comprising:

• providing a composition, the composition comprising:
• a dispersion of pigment particles in a carrier medium, and
• a polyelectrolyte having a net charge controllable from a net positive value at a first pH and a neutral or negative net charge at a second different pH, such that the net charge of the polyelectrolyte has a net charge controllable via adjusting the pH of the carrier medium, wherein, the polyelectrolyte is adsorbed to the surface of each of the dispersed pigment particles forming pH responsive pigment particles, and wherein the net electrical charge of the pH responsive pigment particles is adjustable via adjusting the pH of the carrier medium;
• and,
• applying the composition to the fibres to be treated, wherein the pH of the composition is selected such that the total net charge of the pH responsive pigment particles is opposite to the net surface charge of the fibres to be treated, and thereby colouring the fibres.