Method for producing a plastics moulding (1), wherein in the method a mould insert (3) having a diffractive surface relief (32) is provided, the mould insert (3) is inserted into a mould half of an injection mould (5), said mould half, together with at least one further mould half, forming a cavity for producing the plastics moulding (1), wherein the mould insert (3) is inserted into the injection mould (5) such that the diffractive surface relief (32) forms a subregion of the surface, formed by the mould half (5), of the cavity, and the plastics moulding (1) is moulded by injection-moulding by means of the injection mould (5). The invention furthermore relates to a mould insert and to an injection mould for such a method, and also to a plastics moulding produced in such a way.