Compositions containing(a) at least one 1,4-diketopyrrolo[3,4-c]pyrrole of the formula I, II, IIa, III or IV ##STR1## and (b) an auxiliary redox system from the ferrocyanide, ferrocene or ammonium iron(II) sulfate series in combination with at least one conductive salt (c), where, in the formula I,R and R.sub.2 are, for example, --H and R.sub.1 is --SO.sub.3 Na,in the formulae II and IIa, R and R.sub.3 are, for example, --H, R.sub.1 is --SO.sub.3 H and p is 3,in the formula III, R.sub.4 and R.sub.5 are, for example, phenyl and R.sub.6 and R.sub.7 are, for example, methyl, andin the formula IV R.sub.8 and R.sub.9 are, for example, phenyl,are suitable as electrochromic materials in display systems.