Confirmed for 13w41bThe potion particle effect on the mob is even displaying the right color. Throwing another potion at the mob with lower amplifier/time at the mob seems to activate the effect.This could be used as a workaround:
/summon ThrownPotion ~0 ~1 ~0 {Potion:{id:373,Damage:1337,Count:1,tag:{CustomPotionEffects:[{Id:2,Amplifier:0,Duration:100}]}}}
Confirmed for 13w41b
The potion particle effect on the mob is even displaying the right color. Throwing another potion at the mob with lower amplifier/time at the mob seems to activate the effect.
This could be used as a workaround: