Cleaning Wax Stains from the Ear Mold
Earmolds become stained because the wax and oils from your ear get into the pores of the surface of the mold. This tends to occur more with soft materials like vinyl and silicone, but is, unfortunately, likely to occur with all earmold materials to some extent. Stronger cleaning solvents like rubbing alcohol should NOT be used as they can damage the earmold material and lead to premature shrinkage or tearing.
In my clinical experience the best approach is to wipe the molds daily as you have been doing, but in addition, remove them from the hearing aid ear hook once a week and soak them in hot water for 10 minutes. Allow them dry over night or place them in an active desiccant like the Dry and Store before replacing them on your hearing aids.
Be advised that it is normal for earmolds to have a slight odor, but if there is a strong foul odor, an external ear infection may be present. Please see a hearing healthcare professional if you think you may have an external ear infection.
Finally, if these stains are really bothering you, you can ask your hearing care professional if disposable earmolds may be appropriate for your hearing loss and hearing aid.