The Flashback clothing line was created by a California local music producer and disc jockey, Chis Holmes. He told CBS LA he got the idea for the "retro-reflective material," while touring with Sir Paul McCartney. Holmes was wearing a pair of shoes made of the material and noticed that it ruined photos.
A camera with a flash can't compensate for the brightness of the ultra-reflective material. That causes it to turn pure white, while causing everything else in the photo to be blacked out. It's similar to the shiny parts used in stop signs, for example.
"The idea originally was, you know, to kind of give people more control over whether or not they're photographed. Pretty much everywhere you go, everybody's got their camera out. Everybody's waiting for a crazy moment to capture to post online," Holmes told CBS LA.