system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: Why do things (walls, paper, art, etc) turn yellowish as they age? Why not blue or red or black?

Earlier today I was looking at an old newspaper that had become yellowed and I wondered why most everything I've seen left to age fades the same. Sometimes more pale yellow and sometimes a stronger yellow but I never see anything age in a different hue. 

Is there a specific reason for this?
gpt
Colors are the product of chemicals that have many staggered double bonds in them.  When light hits a compound with these double bonds, it reflects a specific color back to you.  Over time, these chemicals oxidize and when light hits that oxidized chemical, you get the yellowing.  Yellow is the most oxidized compound reflecting light back whereas the darker colors are the least.