1. A method for dying keratin fibres, particularly human keratin fibres, and more particular hair, characterized in that that when it is used, an extemporaneous mixture is applied on the keratin fibres and comprising three steps: - a composition (A) containing one or more oxidation dye precursors and optionally one or more dying couplers in a medium, suitable for dying, - a composition (B), in powder form, containing one or more direct dyes, optionally dispersed in an organic pulverulent excipient and/or a mineral pulverulent excipient, and - a composition (C) containing one or more oxidizing agents in a medium, suitable for dying. 2. The method as claimed in claim 1, characterized in that the direct dye, contained in a powder composition (B) is selected from nitro benzenic colorants, nitropyridines, anthraquinonic colorants, mono- or di-azonic, azinic, acridinic and xanthenic, and also metal-containing dyes. 3. The method as claimed in claim 1, characterized in that the direct dye, containing in the powder composition (B) is cationic ention also features a ready-to-use composition of three components (A), (B), and (C) stored separately and mixed at the time of use to be applied on keratin fibres. 4. The method as claimed in claim 3, characterized in that the dye is chloride 3-[(4-amino-6-bromine-5,8-dihydro-1-hydroxy-8-imino-5-oxo-2-naphtalenyl)-amino]-N,N,N-trimethyl-benzenaminium. 5. The method as claimed in claim 3, characterized in that the dye contains quaternized, optionally desired delocalisable a nitrogen atom and a bond -Z=N-, wherein Z is a nitrogen atom or a radical -CH- 6. The method as claimed in claim 5, characterized in that the dye is a compound of formula (IV): [A-Z=N-B]<+>X<->           (IV) wherein Z is a nitrogen atom or a radical -CH- , A and B are benzene or heterocyclic aromatic groups optionally substituted, X is an anion, whereby a cationic charge has one of substituents of cycle A and/or cycle B. 7. The method as claimed in claim 6, characterized in that the dye is a compound selected from compounds of formulae (10)-(14):   that is chloide 4-amino-phenyl-azo-2-hydroxy-8-trimethylammonio-naphtalene;   that is 2-methoxy-phenyl-azo-2-hydroxy-8-trimethylammonio-naphtalene;   that is 4-amino-3-nitro-phenyl-azo-2-hydroxy-8-trimethylammonio-naphtalene,   that is 3-trimethylammonio-phenyl-azo-N-phenyl-3-methyl-5-hydroxy-pyridazine,   that is chloride 3-[(4,5-dihydro-3-methyl-5-oxo-1-phenyl-1H-pyrazol-4-yl)-azo]-N,N,N-trimethyl-benzenaminium. 8. The method as claimed in any one of preceding claims, characterized in that in the powder composition (B) the direct dye contains from 0,1 to 100 % wt of the total mass of the composition. 9. The method as claimed in any one of preceding claims, characterized in that in the composition (A) the oxidation dye precursors are selected from ortho- or paraphenylenediamines, bis-phenylalkylenediamines, ortho- or paraaminophenols, heterocyclic bases, and acid additive salts thereof. 10. The method as claimed in any one of preceding claims, characterized in that in the composition (A) the oxidation dye precursors contain from 0,0005 to 12 % wt of the total mass of the composition. 11. The method as claimed in any one of preceding claims, characterized in that in the composition (A) the oxidation dye precursors are selected from metaphenylenediamines, metaaminophenols, les metadiphenols, heterocyclic dying couplers and acid additive salts thereof. 12. The method as claimed in any one of preceding claims, characterized in that in the composition (A) the dying couplers contains from 0,0001 to 10 % wt of the total mass of the composition. 13. The method as claimed in any one of preceding claims, characterized in that in the composition (A) the acid additive salts of the oxidation dye precursors and dying couplers are selected from hydrochlorides, bromine hydrates, sulfates, tartrates, lactates and acetates. 14. The method as claimed in any one of preceding claims, characterized in that in the composition (A) further contains at least one reducing agent. 15. The method as claimed in claim 14, characterized in that in the composition (A) a reducing agent is selected from sodium bisulfite, thioglycolic acid and salts thereof and amounts from 0,05 to 3 % wt of the total mass of the composition. 16. The method as claimed in any one of preceding claims, characterized in that in the composition (C) a reducing agent is selected from hydrogen peroxyde, urea peroxyde, bromates of alkali metals and persels. 17. The method as claimed in claim 16, characterized in that an oxydant is hydrigen peroxyde solution, the concentration of which ranges between 5 to 40 volumes. 18. The method as claimed in any one of preceding claims, characterized in that in the powder composition (B) the direct dye is dispersed in an organic pulverulent excipient and/or a mineral pulverulent excipient. 19. The method as claimed in claim 18, characterized in that the excipient is wooden sawdust. 20. The method as claimed in any one of preceding claims, characterized in that relatives quantities of compositions (A), (B) and (C), per weight portions is from 1/0,010/0,5 to /1/4. 21. The composition ready to be used containing 3 compositions as defined in the preceding claims, stored separately and mixed at a timeof use to be applied on keratine fibers. 22. The composition as claimed in claim 21, characterized in that pH of this composition changes from 3 to 12. 23. A kit for dying keratine fibres having a plurality of compartments, characterized in that comprises at least 3 compartments, the first of the is for composition (A) as defined in claims 1, 9-15 and 20, comprising at least one oxidation dye precursors and, optionally, at least one dying couplerin a medium, suitable for dying, the second compartment is for composition (B) as defined in claims 1-8 and 18-20, as powder, containing at least one direct dye as powder or disperse in organic and/or mineral pulverulent excipient, and the third compartment is for composition (C) as defined in claims 1, 16, 17 and 20, containing at least one oxydant in a medium, suitable for dying.