The invention relates to the dyeing of human keratin fibres, especially the hair, using cationic direct dyes bearing a particular sulf(on)ate, carboxylate, or phosph(on)ate counterion of formula (I) in which formula (I) Col(&minus)m, X&minus, m and n are as defined in the description. The invention relates to a dye composition comprising a cationic dye of formula (I), and to a process for dyeing keratin fibres such as the hair, using the said composition. Similarly, the invention relates to novel cationic compounds of formula (I) and to the uses thereof for dyeing keratin fibres. This composition makes it possible to obtain chromatic, powerful and particularly fast coloration on keratin fibres and particularly lightening coloration via an optical effect on dark hair. Col(+)m[X&minus]n&emsp&emsp(I)
