This factor is the relatively slow thermal degradation of colorants and paper that occurs even at room temperature. Historically called "dark fade" because traditional silver-halide photos could change significantly even when stored in the dark, this factor also applies to displayed photos. The accelerated test requires long-term tests of more than a year at several elevated temperatures (e.g., 55ÞC-70ÞC). The results are then extrapolated to a room temperature (e.g., 25ÞC) prediction.
Image result for sublimation textile
Fortunately, ink jet colorants (dye and pigment) are very stable and typically can last 100+ years at room temperature, so dark fade is usually not a limiting permanence factor for ink jet photo prints as long as high-quality sublimation transfer paper is used. Thermal degradation was historically a significant issue for traditional color silver-halide photos due to residual chemicals from the development process. Wilhelm-Research.com has published a variety of thermal degradation data for ink jet and silver-halide photos. Dye sublimation photos cannot withstand the elevated temperatures required by the accelerated test, so long-term longevity is unknown at this time for dye sublimation prints.