It has to be something they are exposed to because mine are very pink when they arrive from the breeder but turn stark white in 4 to 6 days without molting. I've tried different temperature and humidity levels as well as changing the color of the plants, adding pink flowers or just greenery. The best result I've ever had was a slight pinkish tinge in the center of the lobes on their back legs. This occured when I raised the temperature from 76° to 80°F. Raising the temperature to 82° then 84° did not increase the pinkness further. The starting ambient humidity level where I live is usually between 50 to 85% and I mist lightly every day or every other day depending on how high the humidity is to start with and if the substrate has dried out.
Maybe it has to do with the diet of the feeder insects. Flamingos are pink because the shrimp and blue-green algae they eat contain beta carotene. You can also increase red coloration in fish by feeding them fish food with shrimp or krill added. Perhaps giving the feeder insects something high in beta carotene might help? Maybe feed roaches or crickets color enhancing fish food or other sources of beta carotene such as dark green leafy veggies, broccoli, red pepper, papaya, sweet potatoes, carrots and other red or yellow fruits & vegetables. I feed my orchids mainly flies, starting from fruit flies to house flies then finally blue bottle flies and I don't think the fly's food has very much if any beta carotene in it. That might explain the loss of pinkness.