pyrimidine derivative of the general formula i in which r 1 r 2 r 3 and r 4 may be identical or different and are hydrogen oh nh 2 or a group nr 5 r 6 in which r 5 and r 6 may be identical or different and are c 1 c 4 alkyl c 1 c 4 hydroxyalkyl having a primary and or secondary hydroxyl group where two of the radicals r 1 r 2 r 3 or r 4 together can form an optionally substituted 5 and 6 membered heterocycle containing one or two nitrogen and or oxygen atom s in the molecule with the proviso that at least two of the radicals r 1 r 2 r 3 or r 4 are a group nh 2 and or nr 5 r 6 b at least one compound chosen from the group consisting of the a m phenylenediamine derivatives of the general formulae ii or iii b m aminophenol derivatives of the general formula vi c pyridine derivatives of the formulae vii or viii d resorcinol derivatives of the formula ix e methyldioxybenzene derivatives of the formula x or f 3 4 diaminobenzoic acid which are shown above the present invention also further provides a method of dyeing keratin fibers in particular human hair in which a dyeing agent comprising a at least one pyrimidine derivative of the general formula i in which r 1 r 2 r 3 and r 4 may be identical or different and are hydrogen oh nh 2 or a group nr 5 r 6 in which r.