Did you boil the water? Get that water as humanly hot as possible and with black dye just use the whole packet in only about a half gallon of water. Let sit for at least a day or 2. Bones STF's took 4 days and it was still faint. Nav's dyes Spitfire Classics over the course of a month. So be patient. It ain't gunna be a quick thing.
The softer the wheel, the better it will dye, the harder the more dense it is and harder to get color into the urethane.
I've dyed a bunch of sets and the wheels that took the best dye job were 97a Powell wheels. They were perfectly a bright blue in a day.
Harder wheels you need more time, and more dye. In the end it's a pain, but it can be done.
Good luck dude and be patient!