2. Color dyes in color photos are mostly organic molecules with complex structures, which are lively in nature and will decompose in strong sunlight and humid and sultry environment. So once improperly kept, it will make the color photos fade.
3. In addition, if the color photo encounters some highly oxidizing chemical reagents, it will also promote the decomposition of dyes on the color photo and make the color of the color photo fade. Color photos sometimes appear color cast. This is because the dyes in color photos are composed of three different colors of dyes, and the degree of fading of these three dyes is different under the same illumination or the same chemical reagent. So once some colors are changed, there will be color cast.