Some cards just changed their frame look during my game.

I've occasionally noticed that too. A card would appear white in my character's hand, and normal (purple) in the vault/gallery.

 

Seems like it is just a quirky rendering bug in-game.  The card still played as expected, just briefly displayed funny.

 

 

I thought this was intended. All the treasure  cards I currently have in my deck render with the white/silver border, and any new ones get the proper color. Thus I thought they did that so you could tell new treasure from old treasure during the game.

So you say cards could faded after a while.. It could be, but better if devs confirm that

+1 I've had treasure cards (temporarily) display with a white border