'Rainbow fentanyl' is a powdered opioid that can be dyed in a range of colors.
Investigators say the powder can expand in the air, and it could be deadly if it's inhaled.
The blue powder is believed to be more dangerous and more potent than fentanyl pills.
Officials worry the colors could make the drugs more attractive to children.
They're warning parents to communicate with their kids to avoid an accidental overdose.