It is for women 50 and older. It came about because of a line in a poem, that goes something like "When I am an old woman, I shall wear purple with a red hat that doesn't match." There are groups all over now of women who just like to get together with the girls to go out to lunch, shows, etc. If you are under 50, you have to wear lavender with a pink hat.
I'm going to need a new winter coat next year, so I'll just have to get myself a purple one, and a red hat!