Chromatic sunshade cladding unit

The present invention relates to sunshade units for internal or external cladding of the transparent structures of a building façade comprising a plurality of lamellae (201) each having a substantially flat and elongated conformation along a respective development axis (B), and a structure (220,220') supporting the lamellae configured to support the plurality of lamellae (201) in a condition of parallel and spaced apart lamellae along a direction orthogonal to the development axes (B), the structure (220,220') supporting the lamellae being configured to support the plurality of lamellae (201) in a rotatable manner about a rotation axis parallel to or coincident with its development axis (B), characterized in that each lamella (201) of the plurality of lamellae (201) includes at least one surface portion which comprises at least a reflective layer (10) having at least one reflective surface (11), and a chromatic diffusion layer (20) having a first surface (21) proximal to the reflective surface (11) and a second surface (23), opposite and substantially parallel to the first, configured to be illuminated by incident light, wherein the chromatic diffusion layer (20) comprises a nano-pillar (70) or nano-pore (30) structure in a first material having a first refractive index (n1), immersed in a second material having a second refractive index (n2) other than the first (n1), in which the first and second materials are substantially non-absorbing or transparent to electromagnetic radiations with wavelength comprised in the visible spectrum, wherein the ratio ( nM/nm > between a higher refractive index (nm) and a lower refractive index (nm) chosen between the first (n1) and the second (n2) refractive indexes is comprised between 1.05 and 3, wherein the nano-pillars (71) or nano-pores (31) locally have a development along a main direction not parallel to the first surface (21) and to the second surface (23) of the chromatic diffusion layer, and the nano-pillar (70) or nano-pore (30) structure is characterized by a plurality of geometric parameters comprising a pillar diameter or pore diameter (dP), a pillar length or pore length (lp) along said non-parallel direction, a surface density of nano-pillars or nano-pores (Dp) and a porosity (Pp) of structure (30,70), and wherein the plurality of geometric parameters is configured to provide a higher regular reflectance for wavelengths of the incident light comprised in the range of red with respect to wavelengths of the incident light comprised in the range of blue and a higher diffuse reflectance for wavelengths of the incident light comprised in the range of blue with respect to wavelengths of the incident light comprised in the range of red.