system
Given the following post, respond as if you're commenting on Reddit:
human
How do things "fade"- what is happening to the color molecules?

I was going through some old items and boxes- some things were faded from the sun and some things were just faded. What is going on in both cases?
gpt
The molecule that was responsible for colour has reacted to form a different molecule. One common example is in organic dyes - the conjugated pi system is what gives the sharp colour, so when those bonds are broken, the colour disappears. Some reactions simply occur as time passes, while others occur under the presence of UV light, which can excite electrons and make the molecule more reactive.