Kodachrome , dating to the first third of the 20th century, appears most stable and examples exist that are half a century old. Most recently, new techniques, along with some old ones, are creating what is called permanent color prints. The old fashioned dye transfer process has been reintroduced by two small companies. New printing methods using computer-generated thermal dye prints, digital images, supposedly highly stable pigments, and other technology claim to offer permanency for color media. It remains to be seen whether these claims can be substantiated.
Digital permanence is still a matter of speculation.
Jeff Rothen-berg in an article in Scientific American has recently raised disturbing questions about the longevity of electronic media.