Spray mulch dye — experience?

I don’t use dyed mulch, but I might start thinking about it. Many of my customers like dark brown mulch. So do I. I get frustrated when the triple milled hardwood mulch looks a good bit lighter a month after installation.

although I’ve never used it, using a topical spray dye just doesn’t seem like it would work well. Does it for you? What’s your experience been with it?