Process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated, in one or more steps, with one or more cosmetic compositions containing, taken together or separately in said composition(s), the following ingredients: a) one or more dyes chosen from synthetic direct dyes and/or dyes of natural origin, preferably chosen from ortho-diphenols (ODPs); b) one or more titanium salts; optionally b1) one or more carboxylic acids of formula below: formula and a salt thereof, in which: - A represents a monovalent group when n has the value 0 or a polyvalent group when n is greater than or equal to 1, saturated or unsaturated, cyclic or non-cyclic and aromatic or non-aromatic hydrocarbon-based group comprising from 1 to 50 carbon atoms which is optionally interrupted with one or more heteroatoms and/or optionally substituted, in particular with one or more hydroxyl groups; preferably, A represents a monovalent (C 1 -C 6)alkyl group or a polyvalent (C 1 -C 6)alkylene group optionally substituted with one or more hydroxyl groups; - n represents an integer between 0 and 10 inclusive; preferably, n is between 0 and 5, such as 0, 1 or 2; c) one or more cellulose-based polysaccharides; d) optionally one or more organic compounds that are liquid at 25°C with a Hansen solubility parameter value δH of less than 16 (MPa) 1⁄2 at 25°C; and e) optionally one or more chemical oxidizing agents chosen especially from hydrogen peroxide or one or more hydrogen peroxide-generating systems. a) one or more dyes chosen from synthetic direct dyes and/or dyes of natural origin, preferably chosen from ortho-diphenols (ODPs); b) one or more titanium salts; optionally b1) one or more carboxylic acids of formula below: formula and a salt thereof, in which: - A represents a monovalent group when n has the value 0 or a polyvalent group when n is greater than or equal to 1, saturated or unsaturated, cyclic or non-cyclic and aromatic or non-aromatic hydrocarbon-based group comprising from 1 to 50 carbon atoms which is optionally interrupted with one or more heteroatoms and/or optionally substituted, in particular with one or more hydroxyl groups; preferably, A represents a monovalent (C 1 -C 6)alkyl group or a polyvalent (C 1 -C 6)alkylene group optionally substituted with one or more hydroxyl groups; - n represents an integer between 0 and 10 inclusive; preferably, n is between 0 and 5, such as 0, 1 or 2; - A represents a monovalent group when n has the value 0 or a polyvalent group when n is greater than or equal to 1, saturated or unsaturated, cyclic or non-cyclic and aromatic or non-aromatic hydrocarbon-based group comprising from 1 to 50 carbon atoms which is optionally interrupted with one or more heteroatoms and/or optionally substituted, in particular with one or more hydroxyl groups; preferably, A represents a monovalent (C 1 -C 6)alkyl group or a polyvalent (C 1 -C 6)alkylene group optionally substituted with one or more hydroxyl groups; - n represents an integer between 0 and 10 inclusive; preferably, n is between 0 and 5, such as 0, 1 or 2; c) one or more cellulose-based polysaccharides; d) optionally one or more organic compounds that are liquid at 25°C with a Hansen solubility parameter value δH of less than 16 (MPa) 1⁄2 at 25°C; and e) optionally one or more chemical oxidizing agents chosen especially from hydrogen peroxide or one or more hydrogen peroxide-generating systems.