If you go biking at night, it's a smart idea to have reflectors on your bike so cars don't accidentally run you over. But what if, rather than slapping reflectors on your bike, you made your entire bike a reflector? Oh, and you did so invisibly?
This is entirely possible thanks to retroreflective vinyl. It's a material that looks black in normal light, but turns completely white and reflective when a bright light, such as headlights, is shone on it. It's totally awesome, giving your bike a cool black exterior that also keeps you totally safe by acting as beacon when light hits it. You can get the material and do it to your own bike if you want.