Colored mulch could contain dangerous substances, like arsenic or industrial chemical residues. Whether your dog chews on a piece of mulch or licks their paws after digging in it, they could get exposed.  And due to their smaller size, your dog could be at higher risk for ill effects from chemical ingestion.  Consider putting up protective fencing around areas that contain red or black mulch. Not only will your dog stay safer, but your mulch can stay in better condition, too.