Can you ever compliment a stranger's pedicure?

Simple question that I suspect has a complicated answer. Is it ever okay to tell a stranger you like their toenail colour?

Twice in the last month I have been sitting somewhere and noticed a really lovely colour on someone’s toes, in a completely ordinary way, the same way you might notice a good coat. And both times I said nothing, because I could not work out whether it would be friendly or unsettling.

I am a woman, if that changes the calculation, which I suspect it does. Where does everyone draw this line? Does the setting matter more than the words?