The dyes on the wood will be safe. They are either iron oxide (red), carbon (black) or organic vegetable based dyes (brown). It's the wood that the dye is applied to that you need to concern yourself with. It is usually "recycled" wood if it came in a bag. It could be old railroad ties that had creosote on them or end of life pressure treated wood, the old kind that used cyanide based preservatives. If you bought it bulk from a mulch manufacturer then they would have dyed it on site on their own product and you could ask them what they used. Around here, our local mulch manufacturer dyes double shredded hardwood barks.
