Abstract: The present invention relates to a moulded object made of a transparent and coloured plastic exhibiting a polychromatic effect, characterized in that the transparent plastic comprises from 0.1 to 1500 ppm of at least one fluorescent dye and from 50 to 10 000 ppm of at least one optical brightener. It also relates to the resin used for forming the moulded object. It also relates to a light device combining the said moulded object with at least one artificial light source which exhibits an emission in the region of excitation of the optical brightener, in particular in the 300-450 nm range, preferably 350-420 nm range, more preferably still 350-400 nm range.