A process for dyeing or lightening human keratin fibers, which consists of mixing two compositions (A) and (B) extemporaneously at the time of use and applying the mixture to the fibers； said mixture comprising at least 25% by weight of fatty substances in relation to the total weight of the mixture of the compositions (A) + (B): * the composition (A) 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 atmospheric pressure (ii), and that is a saturated or unsaturated long chain aliphatic alcohol comprising from 6 to 34 carbon atoms and comprising at least one OH hydroxyl group, and which is neither mono- or polyoxyalkylene or mono- or polyglycerol； - at least one fatty ester that is solid at room temperature and 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 from 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 alkalizing agent (v) and at least one dye (vi) chosen from oxidation dyes and direct dyes, and mixtures thereof: * the composition (B) comprising at least one oxidizing agent ..Un procedimiento para teñir o aclarar fibras queratínicas humanas, que consiste en mezclar extemporáneamente en el momento del uso dos composiciones (A) y (B) y en aplicar la mezcla a las fibras； comprendiendo dicha mezcla por lo menos 25% en peso de sustancias grasas en relación con el peso total de la mezcla de las composiciones (A) + (B): * estando la composición (A) en la forma de una emulsión directa que comprende: - por lo menos 30% en peso de aceite(s) (i)； - por lo menos un alcohol graso que es sólido a la temperatura ambiente y a
