Just an update for anyone like me who is new to cross stitching and were as confused about this as I was lol. Here are a few things I've figured out from tips I got here and things I've researched:
As you can seen the whole needle is black now except for the tip and the eye.
Cleaning did not help. I think it actually made it corrode faster.
As several people have said, once it corrodes it becomes more difficult to use as it doesn't glide at all anymore. It's not terrible with 14 count Aida, but anything smaller would probably be a real pain to use it with.
Gold plate needles will NOT fix this issue. In fact, everything I've read online says they will actually corrode much faster. There are good reasons to pay for gold plated needles, but this is not one of them.
I did find a company online that sells stainless steel non corrosive cross stitch needles, but they cost almost NINE US DOLLARS PER NEEDLE... ๐ญ๐ญ๐ญ
So ultimately it seems if your needle turns black, your best bet is to just keep using it until it becomes difficult to do so, then just throw it out/repurpose it, and use a new one!
Have you tried polishing? You can usually just take a bit of flitz or similar metal polish and just roll the needle around on a flat surface with your finger and get the surface smooth, even if not all the oxidation gets removed.
But yeah, needles aren't expensive enough to worry about, it would only be for frugality and the RRR factor.
My grandma would just reserve blackened needles for dirty work like patching up my grandfather's coveralls that he would use when working on a car or whatever and tear something enough that it needed repair before washing.
I did try polishing! It did smooth out the needle slightly, but it only lasted about 2 days before the texture got rough again