If you hold it up to the light, you'll see that it's a white card with a sticker or stamp on it.
Seriously, I use those as backing to mini cards when they're in binders so when regular size cards are on the opposite side you won't see part of another card, so they do come in handy.
Follow my blog - I Identify as a Card Collector.
“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis