The present invention relates to a composition (a) or of lightening dyeing of keratin fibers in the form of a microemulsion comprising: (i) at least of the water, ii) at least one oil, the total content of oil (s) being greater than or equal to 5% by weight relative to the weight of the composition iii) at least one surfactant, the total content of surfactant (s) being less than or equal to 19% by weight relative to the total weight of the composition, and iv) at least one compound chosen from among: a. the coloring agents chosen from the direct dyes, the oxidation dyes and / or their mixtures and b. the oxidizing agents, c. the alkaline agents and their mixtures, v), optionally at least a liquid organic compound having a value of δh hansen solubility parameter markedly greater than 0 and less than 16 mpa 1 / 2 l. this invention also relates to a process for dyeing or of the lightening of keratin fibers comprising applying a composition a, optionally preceded by a mixture with a composition b containing at least one oxidizing agent, as well as a multicompartment device, and as a ready-to-use composition, resulting from the mixture of the compositions (a) and (b)). The composition according to the invention makes it possible to lighten or dye keratin fibers such as powerful, effectively, and the homogeneous, while being stable, and easy to apply.La présente invention a pour objet une composition (A) de coloration ou déclaircissement de fibres kératiniques sous forme dune microémulsion comprenant :i) au moins de leau,ii) au moins une huile, la teneur totale en huile(s) étant supérieure ou égale à 5% en poids par rapport au poids de la compositioniii) au moins un tensioactif, la teneur totale en tensioactif(s) étant inférieure ou égale à 19%en poids par rapport au poids total de la composition, etiv) au moins un composé choisi parmi :a. les agents colorants choisis parmi les colorants directs, les colorants doxydation, et/ou leurs mélanges etb. les agents oxydants,c.
