FTM's/transguys: soft packer care?

I have a cyberskin soft-packer that I have modified to be a STP device. I sterilise it regularly but I've found that a couple of years wearing it with dark underpants has stained it, and now it's more grey than pink. No amount of cleaning seems to get rid of the stain. I'm afraid to use bleach in case it gets damaged, and they cannot be boiled as they will melt. Is there any way to restore it's original colour or is it doomed for the trash?