Ishihara Test by Liam Levanon
They see 5 cards, front and back. They're all CLEARLY grey. After a "color-blindness test", somehow they can finally see their super bright colors. Everything is examinable!
Backfire by R. Paul Wilson (CARDS INCLUDED)
Cards switch one-by-one, until the brain-snapping finale. Paul Wilson's masterpiece, better than ever. The ingenious cards do ALL the work.