The invention relates to a process for enhancing the contrast of colour filters comprising a copper phthalocyanine or e copper phthalocyanine, wherein a 1,4-diamino-anthraquinone dye or 1,9-annellated derivative thereof, of which the most bathochromic solution absorption peak in the visible spectrum is at from 575 to 615 nm, preferably at from 585 to 605 nm (as compared with around 630 nm for usual 1,4-diamino-anthraquinone dyes or 1,9-annellated derivatives thereof) is used in combination with a copper phthalocyanine or e copper phthalocyanine. Also claimed are colour filters comprising such 1,4-diamino-anthraquinone dyes or 1,9-annellated derivatives thereof, as well as a novel compound the of formula below, wherein R16 is halogen, phenyl, benzyl or C1-C8alkyl and R17 is H, R16 is H and R17 is C1-C8alkyl, or R16 and R17 are both H; R18 is H, halogen, C1-C8alkyl or SO2NR13R14; R19, R2O and R21 are each independently from the others halogen or C1-C8alkyl; and R22 is independently from R18 SO2NR13R14, with the proviso that at least one of R18 and R22 is SO2NR13R14, and two radicals of formula (II) can optionally be linked together via a direct bond or a group -O-, -S-, -NR14-, -CO-, -CO2-, -CONR14- or -CO2- connecting together each a substituent R16, R17, R18, R19, R20, R21 and R11 from both radicals of formula (II).