You don't need brown or black hulls to dye traps. The green hulls contain more tannic acid than the rotting ones do.
The following is by Tman member NorthCounty
My process produces coal-black traps in less than a 5-minute soak.
I take green walnuts, usually picked off the limbs or fresh drops. Whack them with a plastic mallet, remove and throw away the nut. I fill a mesh sack with approx 4-gallons of the green hulls. Tie the sack shut, place in steel drum and cover with enough water to fit 18-trap batches on top of sack. I heat the drum of water + hulls with a propane burner, and "brew" it for about 1 hour. At this time the water is jet black. Immerse a batch of traps for about 5 minutes, setting them right on top of the sack, which is still on the bottom of the drum. Let the traps simmer for 5-mins (longer doesnt hurt anything), remove and set on a pallet to dry. I can process well over 150 traps and still have a perfect, thick, jet black coating on the last batch. In fact I have never found the point at which the solution becomes weak.