Not all dyes can be discharged. Some dyes will retain their color no matter what chemical or conditions you use to try to strip the dye. Others will change to a completely different and unexpected color. It is impossible to predict whether the dyes in a specific garment are possible to remove, because you never know which dyes were used to color it. Even if you successfully discharge a hundred identical garments from a specific wholesaler, the hundred-and-first garment might fail to lose its color, due to an undisclosed change in the formula of the dye that was used to color it.

"You cannot use dye to whiten a garment which has already been dyed. Instead, you need to remove the dye that is already there. There are many different chemicals which can be used to remove dye: see "What chemicals can be used to remove dye?". All of these chemicals have the potential for damaging your fabric. 

"You should never use hypochlorite (household chlorine bleach) on nylon, because it will damage or destroy the fiber. It is possible, however, to use sulfur-based discharge chemicals on nylon, using care to prevent damage. PRO Chemical & Dye provides instructions for using their product Formosul (sodium formaldehyde sulfoxylate) to remove dye from nylon. Rit Color Remover (sodium dithionite plus sodium carbonate) has also been used successfully to remove some dyes from nylon. Both of these products can be used at home. Follow the manufacturer's instructions carefully. Rit Color Remover works better in a dyepot (not made of aluminum or iron) on the stovetop than it does in hot tap water in the washing machine, but in many cases the washing machine method is adequate, and certainly more convenient. (See the instructions for the stovetop method for Rit Color Remover in this May 2006 Dye Forum posting.)"