Coloured PVB

A process for modifying the color in transmission of an optical system from an initial state having an initial color (L*i;

• a*i;
• b*i) to a final state having a final color (L*f;
• a*f;
• b*f), said process comprising at least one step of modifying the absorbance properties of an optical element of said optical system so that at least 50% of the total absorption (A) of said optical element occurs in an effective absorption range ([λmin;
• λmax]) defined so that a variation in absorption by the optical system of any amount of light at a wavelength λ comprised in said effective absorption range ([λmin;
• λmax]) generates a variation ΔC(λ) in chromaticity distance (Ci, C(λ)) smaller than 0, where:
• ΔC(λ)=C(λ)−Ci=√{square root over ((a*(λ)−a*ref)2+(b*(λ)−b*ref)2)}−√{square root over ((a*i−a*ref)2+(b*i−b*ref)2)}
• (Ci, C(λ)) is the chromaticity distance between a given value ((a*i;
• b*i), (a*(λ);
• b*(λ))) of chromaticity in transmission and a reference value (a*ref;
• b*ref) of chromaticity in transmission,
• (a*i;
• b*i) is the initial value of chromaticity in transmission,
• (a*(λ);
• b*(λ)) is the value of chromaticity in transmission obtained following the variation in absorption achieved at the wavelength λϵ[λmin;
• λmax].