The effect that can be seen on stickers covered with a convex layer of polyurethane resin is the illusion of mixing colors that are printed on the film. An example is the illusion of making a pink background when using red elements on a white background. In the picture before pouring the sticker on the resin you can see that the background color is white, only the resin acts like a prism and creates the illusion of mixing paints (you can see around the red rectangle in the picture attached).