The electrochromic system proposed contains at least one oxidizable substance RED1 and at least one reducible substance OX2 each of which changes from a colourless or only slightly coloured form into a coloured form by virtue of an increase in the absorbance in the visible region of the spectrum. The system is characterized in that the conversion of the oxidizable form into the reducible form and vice versa occurs by cleavage or formation of a sigma -bond.
