Fenestra Tarot, Royalty cards

cookienin

I was laying out the Fenestra Tarot along side the Rider Waite Smith Tarot and noticed something I haven't seen pointed out yet. When I was comparing the royal houses I noticed that in Fenestra Tarot there is a unique difference from the rest of the deck. The titles on the cards have a whitish grey background. I noticed this made them stick out from the rest of the deck. The Major Arcana does not share this or have anything that makes it stick out from the rest other than they have a name along side their numbers. Does anyone have an idea why this is?