I’ve had many questions about the use of dyed colored mulch in landscapes. The truth is this mulch is made from low quality reclaimed wood like pallets and construction waste and it contains dyes and CCA’s.
The CCA’s are the most concerning; Chromated Copper Arsenic is used to prevent insects and fungi from decomposing the wood. These toxins will leach from the decomposing wood and bioaccumulate in your soils.
This is most concerning is if you have children and pets that may ingest the upper layers of soil through contact. It is also harmful to humans that grow leafy vegetables as they hyperaccumulate the toxins in their leaves.
Here’s an article that further explains why they should not be used.