Hi there, I have read in "A Dream of the Red Mansions" (a Qing Dynasty/19th century Chinese novel) that bright red impatiens were used by women to colour their finger nails.

According to one passage in the book, apply the crushed flowers generously on the nails and leave them in place for "a while," then carefully remove the flowers. The finger nails "will be stained."

I haven't tried this so let me know if it works ;-) Have fun!

Yes. This is kind of late but. I have those flowers in my back yard. They're pretty but can take over your yard if you don't control them. Bongsunwah is what they're called in Korean.

Maybe this is the pink flower your Korean neighbour is thinking of: Hydrocera trifolia or water balsam or water henna. See
http://gardeningwithwilson.com/category/flowering-plants/page/2/

My mother is Korean and when I was a little girl, we used to use the rose balsam to color our nails. Happy memories :) She still grows them year after year. The red variety makes the best polish.

Here is a link that might be useful: Rose Balsam