How does the devoid-granting ability of Slivdrazi Monstrosity work?

Question

Slivdrazi Monstrosity grants devoid to all slivers. And then the Gatherer ruling says this:

Due to the carefully calibrated system of layers that Magic uses to determine the interaction of continuous effects, gaining an ability that changes the color of an object has no effect on the color of that object. Despite this, Slivdrazi Monstrosity causes Slivers to become colorless as they gain devoid. Rather than try to figure out how this could work, this card should just be played as though it read “Slivers you control have devoid and annihilator 1 and are colorless.”

Unfortunately for me, I would very much like to figure out how this could work. CE 613.1 says color changing effects are applied in layer 5, and then ability-adding effects in layer 6. So just as the Gatherer ruling says, it very much seems like slivers will stay colorful, but have devoid, as their color is set before devoid is granted.

How does the Monstrosity make slivers colorless? Is it just a case of the above Gatherer ruling standing in as an errata? Or does the Monstrosity's ability, taken at face value, with correct rules interpretations, actually make slivers colorless somehow? And how would that work?

Answer 1

The Gatherer ruling is saying that the card doesn't change Slivers' colors as written, but the intention of the card is to change the colors, so you should play the card as though it does. That is a playtest card, so it is unsurprising that it doesn't exactly work within the rules.

Answer 2

If Slivdrazi Monstrosity was a "real" card, released in a proper set, it would have full rules support. Part of that support involves modifying rules that prevent cards from working how they are intended.

For instance, among the rules changes with the release of Strixhaven was a change to rule 603.3B:

Players paying close attention during preview season noticed that Strict Proctor has an odd trigger condition and effect that wouldn't quite work right under current rules. Sometimes, Strict Proctor's ability would end up placed on the stack underneath the ability it was trying to counter. This rule has been changed to make putting triggers on the stack a two-part process, ensuring that Strict Proctor can always enforce its requirement.

In this case a timing issue existed that could interfere with how a card was obviously supposed to work, so the rule was changed to prevent it. Because Slivdrazi Monstrosity is a playtest card and lacks rules support, Gatherer notes that players should modify the rules in a similar way so that the card can work as intended.