Sometimes, when landing on a carpet block that is being pushed by a sticky piston, the particles emitted will be the 'purple and black' missing texture.
The 'moving_block' should take the attributes of the original block and emit the corresponding particle texture.
How to reproduce:
Set a command block in the sky that will automatically summon pillagers, in a vertical tube (so they don't escape) and place pistons pushing carpets horizontally, back and forth, at the bottom of the tube. Some particles should be 'purple and black' when the mobs land at the perfect moment.