same experience
Woke up in the morning to find rust-like stains on my palms.
I did a liver function test, I asked my doctor, and I suspected jaundice, Gilbert's syndrome, lycopeneemia, caroteneemia, riboflavinemia.
Combining what I have found and the content of this post, I am more inclined to be caused by my hands touching something containing special substances. I never walk barefoot on the ground, and it seems that my feet are indeed fine. I ate a cantaloupe before going to bed last night and it had some pits on the skin and was underripe, so I threw it away after a few bites. The location of the patches on my hands matched the areas where I had contact with the cantaloupe skin, maybe plant sap, maybe bug secretions. Obviously this chemical is insoluble in water and does not react with alkaline substances, so it is difficult to wash off.
The things you have touched may be different, but they should all contain similar chemical compositions.
This is the interpretation I prefer, and it may be wrong.
Sincerely hope you can finally figure this out completely.