A chromatic reflective unit comprising: a reflective layer, and a chromatic diffusing layer having a back side provided at the reflective layer and a front side for being illuminated by incident light so that incident light passing the chromatic diffusing layer is reflected by the reflecting layer and passes the chromatic diffusing layer again, wherein the chromatic diffusing layer comprises a plurality of nanoparticles embedded in a matrix, and is configured to provide for a specular reflectance that is larger in the red than in the blue and for a diffuse reflectance that is larger in the blue than in the red, reflectance being the ratio of the reflected flux to the incident flux in given conditions, wherein: said nanoparticles have an average size d in the range 10nm ≤d≤240nm; the ratio between the blue and red scattering optical densities γ = Log[R(4.50nm)]/Log[R] of said chromatic reflective unit falls in the range 5≥γ≥2.5, where R(λ) is the monochromatic normalized specular reflectance of the chromatic reflective unit, which is the ratio between the specular reflectance of the chromatic reflective unit and the specular reflectance of a reference sample identical to the chromatic reflective unit except for the fact that the chromatic diffusing layer does not contain nanoparticles with the size d in the range 10nm ≤d≤240nm; for the direction normal to the reflective layer of the chromatic reflective unit, the monochromatic normalized specular reflectance R(λ) of the chromatic reflective unit at a wavelength of 450nm is in the range from about 0.0025 to about 0.15, such as defined by the equations 0.0025≤R ≤ 0.15, 0.0025≤R ≤0.05, 0.0025≤R ≤0.04. a reflective layer, and a chromatic diffusing layer having a back side provided at the reflective layer and a front side for being illuminated by incident light so that incident light passing the chromatic diffusing layer is reflected by the reflecting layer and passes the chromatic diffusing layer again, wherein the chromatic diffusing layer comprises a plurality of nanoparticles embedded in a matrix, and is configured to provide for a specular reflectance that is larger in the red than in the blue and for a diffuse reflectance that is larger in the blue than in the red, reflectance being the ratio of the reflected flux to the incident flux in given conditions, wherein: said nanoparticles have an average size d in the range 10nm ≤d≤240nm; the ratio between the blue and red scattering optical densities γ = Log[R(4.50nm)]/Log[R] of said chromatic reflective unit falls in the range 5≥γ≥2.5, where R(λ) is the monochromatic normalized specular reflectance of the chromatic reflective unit, which is the ratio between the specular reflectance of the chromatic reflective unit and the specular reflectance of a reference sample identical to the chromatic reflective unit except for the fact that the chromatic diffusing layer does not contain nanoparticles with the size d in the range 10nm ≤d≤240nm; for the direction normal to the reflective layer of the chromatic reflective unit, the monochromatic normalized specular reflectance R(λ) of the chromatic reflective unit at a wavelength of 450nm is in the range from about 0.0025 to about 0.15, such as defined by the equations 0.0025≤R ≤ 0.15, 0.0025≤R ≤0.05, 0.0025≤R ≤0.04. said nanoparticles have an average size d in the range 10nm ≤d≤240nm; the ratio between the blue and red scattering optical densities γ = Log[R(4.50nm)]/Log[R] of said chromatic reflective unit falls in the range 5≥γ≥2.5, where R(λ) is the monochromatic normalized specular reflectance of the chromatic reflective unit, which is the ratio between the specular reflectance of the chromatic reflective unit and the specular reflectance of a reference sample identical to the chromatic reflective unit except for the fact that the chromatic diffusing layer does not contain nanoparticles with the size d in the range 10nm ≤d≤240nm; for the direction normal to the reflective layer of the chromatic reflective unit, the monochromatic normalized specular reflectance R(λ) of the chromatic reflective unit at a wavelength of 450nm is in the range from about 0.0025 to about 0.15, such as defined by the equations 0.0025≤R ≤ 0.15, 0.0025≤R ≤0.05, 0.0025≤R ≤0.04.