A process is described which consists, in a first stage, in applying a composition based on a substance of vegetable or animal origin, a synthetic organic substance or a mineral substance, in suspension or in solution in a solvent and having a viscosity suitable for application to the hair, or as a powder, and making it possible to prevent or substantially to limit the passage of the dyestuffs and/or of the dyestuff precursors as far as the scalp, and, in a second stage, in dyeing the hair using one or more compositions, at least one of which contains either an oxidizable dyestuff or a direct dyestuff, the dyeing being followed, after an interval sufficient for coloring the hair, by rinsing and optionally by shampooing.