in a predetermined time period -say half a year or a year the change should be an intrinsic property -with no dependence on external factors. Preferably -it should be a material that can be laminated
Reactive dye is the most sensitive material . Use it to dye natural cellulosic material eg CMC and use it as a paste for lamination
There are standard test methods and kit for quantifying the light fading properties of dyes and pigments. The Google query ‘light fastness testing’ is a good starting point. Light fastness is rated on an approximately logarithmic scale from 1 to 8 and testable physical samples representing each grade may be bought from the Society of Dyers and Colorists. The procedure is to expose your product to light alongside an appropriate reference sample. Grade 1 will probably fade after a day or two in direct sunlight and grade 8 will withstand years of such exposure. Accelerated testing with bright light sources, giving a result typically within 24 hours is typical.
Dye and pigment makers often publish light fastness ratings, and the colorant you are looking for is often called a ‘fugitive tint’. Such Companies are in general seeking to sell ‘light fast’ products but it is worth seeking their help in meeting your requirement.
Many yellow pigments will degrade under UV exposure. The addition of some UV filter to the mix can slow this.
I recommend looking at this website for a list of pigments (of all colors). The table has a column for lightfastness.
All natural pigment from animals can fade easly with ageing or under the action of light
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