There is not any trick, just the laws of physics and optics. The human eye tends to note brighter tones and colors about darker. So investigating your indication from the outside the viewer isn't going to recognize the holes - just the graphic impression. Our Rear Window Decal sticker is https://car-rear-window-sticker24679.isblog.net/the-smart-trick-of-sticker-on-the-rear-window-that-no-one-is-discussing-40577369