I have this issue all the time - I purchase my prints from a local baking supplier and I'm struggling now because I have an order where color longevity is critical. I've been told it's a reaction to light and 'it's the nature of the beast' but I can't afford to take a chance. Sometimes the printed color fades and bleeds within 24 hours of application. I thought it might be because the RI wasn't completely dry, but I see from reading other posts that this is not usually an issue with icing sheets.
Going to find an alternate source now. Thanks for this advice!