Here is a link to manufacturer instructions http://hippymulch.com/howtosprayhippiemulch.html
, but what we found that worked great was a battery powered 5 gallon backpack sprayer. Solo has one that runs about $350 and worked fantastic. We also had another sprayer filled with water, one employee wet the rocks, and edging prior to our spraying, then came back after spraying the color and washed down any color that got on those items.
The material cost was about a penny per sqft and we had a crew of three there for only two days to complete the job. We use $30 per man hour to figure our labor so we had less than $2,000 in labor and $2,000 in material cost (you can buy Hippy Mulch online at their website). We charged $10,000, and were the only company that bid a recoloring, were told that everyone else was bidding double our price so they decided to try us.
We also bought a couple $30 hand garden tillers to roll the mulch. We sprayed everything once, tilled the mulch, and re-sprayed.