My sister-in-law Carol is Korean. At a family gathering, Carol said that she didn't understand why all of my mother's houseplants did so well and all of hers died. I said, "That's because Mother has a green thumb and you have a yellow thumb."
When everybody there laughed. Carol asked what was funny.
Humor is oftentimes not easily translatable from one culture to another. Carol asked me to explain why it was funny; I told her that in the United States if someone were good at raising plants then we said that they had a "green thumb" because the plants stayed green.
Carol looked at her thumb and said, "Oh, I get it now--mine don't grow--they turn yellow and die; I have a yellow thumb--oh, it's funny--now I laugh!"