Who came up with the prase blue hairs, and why are old people called that?

It comes from 'blue rinse', a hair-dye used less now, but at one time was a way of glamourizing greying hair to make it appear less yellowish. I remember hearing my mother talking about people having them done, UK early 1950s.

http://en.wikipedia.org/wiki/Blue_rinse

Who came up with the prase blue hairs, and why are old people called that?

The phrase is "blue-haired" --

Years ago hair dyes were very harsh, and many women who had their gray hair tinted came away from the salon with silver hair that had a blue tinge to it.

We refered to those women as "blue-haired old ladies."

For instance: "Louise has put together a Wednesday Tea and Bible study for the blue-haired group."

Who came up with the prase blue hairs, and why are old people called that?

I always thought they chose to have it dyed that colour, I've seen old girls who's hair had more than just a tinge of blue.

Don't think I've seen any recently though.