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?