A method for coloring fibers or fibrous materials where the fibrous material is initially chemically pretreated in order to achieve natural/white color for the fibrous materials. Next the pretreated fibrous material, a polymer base, and the colorant concentrate(s) are combined under suitable conditions to form a biocomposite mixture. The chemical pretreatment of the fibrous material prevents damage from being done to the fibrous material, such that the fibrous material retains its strength enhancing properties when combined with the polymer to form the biocomposite mixture. Additionally, the chemical pretreatment enables the fibrous material to chemically and mechanically bond with the colorant when combined into the biocomposite mixture.