Lemon Juice should do the trick.
It's the citrus acid in it that removes the stains.
I used to work with a lot of mahogany that turned my hands purple.
It works for me,
Jerry

"Clemens" wrote in message
...
I was picking and halving walnuts, and my hands got dark brown from
tannin in walnut's shell.

Please, is there any effective agent to remove dark stains off the
hands ?

I tried with acetone, alcohol, lighter fuel, paint thiner, windex,
washing soap, laundry detergent, but it didn't help.

Thank you.