For more than two decades, Magic: The Gathering cards with a silver-colored border were a bit, well, odd.
They were originally made for Unglued in 1998 in order to help differentiate what cards could be used for tournament play and which ones were for more casual settings.
The difference between black and silver bordered was supposed to be just that: a silver border meant the card couldn't be played in any normal sanctioned format.
But, as the years went by, the fact that they couldn't be played in most official settings wound up putting a certain stigma on them.
Sure, the "Un-" sets were meant to be nothing but fun, but other cards were suddenly getting devalued simply because of the border color.
Wizards R&D, essentially, had a bit of an issue on their hands as, to much of the Magic-playing community, silver bordered cards were not seen as a different subset of Magic, but rather as not even "actual" Magic: The Gathering cards.
After about ten years or so of silver-bordered cards, they weren't even welcome in casual matches in some circles.
Naturally, this was a bit of a problem.
So, in the late 2010s, big changes were on the way. The higher-ups at WotC started looking for ways to make silver-bordered cards as appealing to buy and own as, well, their black and white bordered cousins.
Lucikily, by this time, Magic had begun using holofoil stamps -- typically on rare and mythic rare cards -- as a sort of anti-counterfeiting technology. The company decided to begin using this technology in a different way.
Beginning with the release of Unfinity later this year, acorn-shaped holofoil stamps were put on these "not for tournament play" cards in lieu of the silver border treatment. Of course, rule-sticklers and those who are expecting deckbuilding confusion due to the now-uniform borders more-or-less seemed to be concerned, or even downright dislike this decision.
It will be interesting to see, long term, how things unfold. For now, at least, Magic: The Gathering has "acorny" (Get it? Acorny? A corny? Nevermind.) future.