The present invention relates to a composition for dyeing and/or lightening keratin fibres, in particular human keratin fibres such as the hair, comprising: a) one or more guanidine salts, b) one or more alkanolamines, c) ammonium hydroxide and d) at least two different polyols in a total content greater than or equal to 5% by weight relative to the total weight of the composition, and e) optionally one or more colouring agents. The invention also relates to a dyeing and/or lightening process using said composition, and also to a multi-compartment device which is suitable for using said dyeing and/or lightening composition.