Process for dyeing or lightening human keratin fibres, which consists in extemporaneously mixing at the time of use two compositions and and in applying the mixture to the fibres; the said mixture comprising at least 25% by weight of fatty substances relative to the total weight of the mixture of compositions +; with: * composition being in the form of a direct emulsion comprising: • at least 30 % by weight of oil(s) (i); • at least one fatty alcohol that is solid at room temperature and at atmospheric pressure (ii), and which is a saturated or unsaturated long-chain aliphatic alcohol comprising from 6 to 34 carbon atoms and comprising at least one hydroxyl group OH, and that is neither mono- or polyoxyalkylenated nor mono- or polyglycerolated; • at least one fatty ester, which is solid at room temperature and at atmospheric pressure (iii), and which is chosen from esters of optionally hydroxylated saturated carboxylic acids comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms, and of saturated fatty monoalcohols comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms; • at least one surfactant (iv); • at least one basifying agent (v) and/or at least one dye (vi) chosen from oxidation dyes and direct dyes, and mixtures thereof; * composition comprising at least one oxidizing agent. * composition being in the form of a direct emulsion comprising: • at least 30 % by weight of oil(s) (i); • at least one fatty alcohol that is solid at room temperature and at atmospheric pressure (ii), and which is a saturated or unsaturated long-chain aliphatic alcohol comprising from 6 to 34 carbon atoms and comprising at least one hydroxyl group OH, and that is neither mono- or polyoxyalkylenated nor mono- or polyglycerolated; • at least one fatty ester, which is solid at room temperature and at atmospheric pressure (iii), and which is chosen from esters of optionally hydroxylated saturated carboxylic acids comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms, and of saturated fatty monoalcohols comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms; • at least one surfactant (iv); • at least one basifying agent (v) and/or at least one dye (vi) chosen from oxidation dyes and direct dyes, and mixtures thereof; • at least 30 % by weight of oil(s) (i); • at least one fatty alcohol that is solid at room temperature and at atmospheric pressure (ii), and which is a saturated or unsaturated long-chain aliphatic alcohol comprising from 6 to 34 carbon atoms and comprising at least one hydroxyl group OH, and that is neither mono- or polyoxyalkylenated nor mono- or polyglycerolated; • at least one fatty ester, which is solid at room temperature and at atmospheric pressure (iii), and which is chosen from esters of optionally hydroxylated saturated carboxylic acids comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms, and of saturated fatty monoalcohols comprising at least 10 carbon atoms, more particularly from 10 to 30 carbon atoms and preferably from 12 to 24 carbon atoms; • at least one surfactant (iv); • at least one basifying agent (v) and/or at least one dye (vi) chosen from oxidation dyes and direct dyes, and mixtures thereof; * composition comprising at least one oxidizing agent.