Why does a tamagotchi turn yellow? (Case)

[Sylveon]

I have a tamagotchi that doesn't give it the sun and I always protect it with crochet covers, however I notice how it is losing its color and it is turning yellow... why?

 

[KuroiNeko-Chan]

It's just paint fading.  My 5.5 Celebrity lost its paint, too.  It happens sometimes.  What I want to know is if I could paint it myself and five it a custom shell design.

 

[Penguin-keeper]

Depending on the age of the item, plastic turning yellow is usually due to flame-retardant chemicals in the plastic rising to the surface, causing the discolouration. Contrary to popular belief, it's entirely possible for something only exposed to sunlight once or twice to have this eventually happen.

This doesn't happen with plastics made after a certain time, but it definitely does affect plastics from the 1980s and 1990s, at the very least.

 

[Sylveon]

Well, is a tamagotchi P's and it has never given direct sunlight (it has always been inside the house).
I had it in its box, and when I went to take it out I realized that it was a little yellow (even the heart). It is pink.
I don't understand how it could have happened or how to prevent it from ending up becoming ugly.

 

[N4LLLC]

Just like what PK said, and also the color additive in the plastic is reacting with the plastic.  The pink Angelgotchi  has this problem too.  And we don't know the manufacturing processes to make the shells.  They may be made of recycled and regrind.  This is only a theory, and I'm sorry your p's is doing this.