That's crazy! You'll see the pic in color as long as you keep staring at the black dot long after the 'time' expires but the moment you shift your focus away it'll turn black & white.
Clever use of afterimage and how the human eye heightens colour when it is stared at for a length of time (hence the timer). Try staring at a red or blue object for 20 seconds, for example, and see how other objects this colour stand out.
