The present invention relates to a cosmetic composition comprising, in a cosmetically acceptable medium, a dyestuff comprising a biopolyester comprising repeating units of formula (I):in which R is a saturated C1-C18 alkyl chain, or a hydrogen atom m = 0 or 1 and n is between 450 and 1400and at least one colouring being plasmonic particles.The invention also relates to the dyestuff per se, and to a cosmetic process for treating keratin materials employing said composition.
