A method for producing a composite coloured metal-containing powder, characterised in that said method consists of the following steps, in the absence of surface modifiers: a) preparing a bulk metal-containing material in the form of powder which acts as a particle substrate by means selected from the group consisting of: a.1) grinding or milling a raw metal-containing material into powder, directly; a.2) grinding or milling a raw metal-containing material into powder, and classifying the milled powder into fractions; and a.3) classifying a raw metal-containing material powder into fractions, directly without grinding or milling; wherein the bulk metal-containing material is a ferromanganese powder selected from the group consisting of: a high Carbon FeMn, a refined medium Carbon FeMn and a refined low Carbon FeMn; having an elongated shape and an homogeneous particle size selected from the group of fractions consisting of: 125-250 μm, 60-125 μm, 45-60 μm, 20-45 μm, from higher than 0 μm to 20 μm, and from higher than 0 μm to 10 μm, wherein less than 10% by weight of the powder has a size lower that the lower limit of the particle range, and that less than 10% by weight of the powder has a size higher that the higher limit of the particle range, wherein measurements of the particle size are carried out using a sieve for sizes higher than or equal to 45 microns, and using laser diffraction means for a lower size; and b) heating the bulk metal-containing powder up to a temperature ranging from 100°C to 1000°C in a rotating furnace, in the presence of oxygen during a heating time needed for obtaining the metal-containing powder having one colour selected from the group consisting of: any intermediate tonality between the original colour of the bulk metal-containing powder and gold; gold, violet, blue, and any intermediate tonality between said colours; wherein the heating time is inversely related to the temperature and directly related to the particle size of the bulk powder. a) preparing a bulk metal-containing material in the form of powder which acts as a particle substrate by means selected from the group consisting of: a.1) grinding or milling a raw metal-containing material into powder, directly; a.2) grinding or milling a raw metal-containing material into powder, and classifying the milled powder into fractions; and a.3) classifying a raw metal-containing material powder into fractions, directly without grinding or milling; wherein the bulk metal-containing material is a ferromanganese powder selected from the group consisting of: a high Carbon FeMn, a refined medium Carbon FeMn and a refined low Carbon FeMn; having an elongated shape and an homogeneous particle size selected from the group of fractions consisting of: 125-250 μm, 60-125 μm, 45-60 μm, 20-45 μm, from higher than 0 μm to 20 μm, and from higher than 0 μm to 10 μm, wherein less than 10% by weight of the powder has a size lower that the lower limit of the particle range, and that less than 10% by weight of the powder has a size higher that the higher limit of the particle range, wherein measurements of the particle size are carried out using a sieve for sizes higher than or equal to 45 microns, and using laser diffraction means for a lower size; and a.1) grinding or milling a raw metal-containing material into powder, directly; a.2) grinding or milling a raw metal-containing material into powder, and classifying the milled powder into fractions; and a.3) classifying a raw metal-containing material powder into fractions, directly without grinding or milling; b) heating the bulk metal-containing powder up to a temperature ranging from 100°C to 1000°C in a rotating furnace, in the presence of oxygen during a heating time needed for obtaining the metal-containing powder having one colour selected from the group consisting of: any intermediate tonality between the original colour of the bulk metal-containing powder and gold; gold, violet, blue, and any intermediate tonality between said colours; wherein the heating time is inversely related to the temperature and directly related to the particle size of the bulk powder.