Apple Pencil rear tip became yellow

This is entirely cosmetic - and as such is unlikely to be considered a warranty defect.

Discolouration of plastics is not uncommon - and is generally something that occurs, over time, in white brominated plastics. Generally, plastics that are evenly exposed to moderate UV light retain their appearance better than those continuously shaded from light. Affected objects that are unevenly exposed to UV, in a static position, tend to discolour more on the shaded side.

Here is an external link that describes the effect:

https://medium.com/@pueojit/a-look-into-the-yellowing-and-deyellowing-of-abs-plastics-db14b646e0ad

The plastics used in Apple products tend to better than most, but are not immune.

I hope you find this information helpful.

Return it and see if your Apple Store will give you a new one.

It may have statred yellowing in the box if that Apple Pencil is new, old stock laying around.

Plastics generally do not start yellowing in that short a period of time.

The free, one-year Apple accessory warranty still applies no matter where you purchased.

So, I would try an Apple Store, first. Take your purchase receipt as proof you purchased two weeks, ago.

If they tell you to bring it back to the place you originally purchased, then you will need to do this and you would need the sales receipt for that store, anyways.

Best of Luck to You!

If its still under Apple's one year accessory warranty, bring it into your nearest, “local” Apple Store for a free, in-warranty replacement.

Best of Luck to You!

Try and see if your “local” Apple Store would give you a replacement Pencil, anyways.

If this yellowing bugs you, it is worth a shot.

All they can do is say no.

No problem.

Good Luck to you!