Pick up trick: flashing color

Hey Uber and Lyft, I just had a great idea for you. How about when a driver gets close to their rider, you assign the rider a reasonably unique color and ask them to hold their phone up, facing the street, with the display facing out, flashing that color brightly. Alternatively or additional, give drivers a way to have a programmable display on their car that does something similar. Would make pick ups in busy city areas a lot easier across the board.