A red/green colorblind friend of mine has a pair of glasses that have a sharp notch in their spectral response, at ~550nm (I think), that lets him better see tonal differences across the frequencies "normal" folks interpret as red and green colors. He wears 'em mainly when driving. The effect is less about more colors than about a broader & finer tonal range.
-Dave-
That is the impression I have, too, having read about such lenses. And they are very expensive, so I have never tried them.
For the first fifty years of my photography, my R-G color-deficiency was unimportant. All my serious work was black and white, processed by me, while color (Kodachrome) was sent off to Mother Kodak for processing. When I went over to the (digital) Dark Side, it was great fun to be able to make color prints myself. Then a photographer friend of mine visited an exhibit of mine and let me know that the skies in some of my landscapes were too Cyan. Of course they looked blue to me. From that experience I learned never to adjust color balance in any way in images that ought to be "realistic." For abstract images I am willing to do anything that looks interesting to me.
I was about 16 or so when I learned that I was color-blind. My school library had a book of the Ishihara color vision test charts, which clinched it. Later I learned that my situation was just what Mendel would predict: MY mother's father was color-blind, so my mother had normal vision but was a carrier, and exactly half of her male children were color-blind (my brother is not.)
Of course, it was the color-blind one who got interested in photography.