Double-sided playing cards. One side has a light-colored background and dark lettering, the other side has a dark background and light lettering, and get this: they represent different cards. It’s brilliant.
I know what you’re thinking: people will just memorize which dark cards correspond to which light cards and completely fix the game, but that could never happen. People are generally good at heart, and will always endeavor to do the right thing. It’s that spark of the divine in all of us. That’s why this invention is perfect: because human nature is perfect, too.