an optical security component for authenticating a document or a product including a transparent plastic film embossed to form an embossed surface and to have at least one diffraction grating ; a layer of dielectric material of high optical index at least partially coated on the embossed surface and producing a colored effect of a first color for a first orientation of the component and a second different color for orientation perpendicular to the first orientation ; a low optical index layer coated on a side opposite the viewing direction of the dielectric material ; and a colored contrast layer having transparent zones and colored zones on the low optical index layer .