Turn Flashlight into Black Light with Your Smartphone Here is how: First, you take the tape and fold it on the ends, so it pulls off easily. Then take the first piece of tape, put it over the camera flash on the back of your phone. Color that tape blue. Repeat this step again. After you’ve put both layers of tape onto the flash or light of your camera, put the third and final layer on top of that one. This is where you pull out your purple Sharpie and paint that sucker in. Go crazy.