Lingering potions and Creepers with potion effects that have ShowParticles set to 0 are expected to have the particles of their lingering effect not visible. However, those particles are visible and appear black (no matter what the effect is).

The effect can be recreated with this potion and this /summon command:

/give @p lingering_potion 1 0 {CustomPotionEffects:[{Id:1b,Duration:100,ShowParticles:0b}]}

/summon creeper ~ ~ ~ {Fuse:0s,ExplosionRadius:0b,ActiveEffects:[{Id:1b,Duration:100,ShowParticles:0b}]}