Well, my two cents worth is because the human is is drawn to colors, and is most sensitive to green. The cones are senstive to the bright colors. The rods, on the other hand, are "more" sensitve, and is primarily what you use to see in the "dark". That is why when you are in a dark enviroment you do not tend to "see" very much color.
In your eye the cones are in the center, with the rods being on the outer edge, and you can test this by covering one eye for about 20 to 30 minutes, and then go into a dark room. When you first enter you would notice that the room is almost pitch black. Cover that eye up, and then look with your other eye. You will notice that the room isnt as dark as you thought it was. Your covered eye has become dark adapted, and if you look out of the "corner" of your eye, you can see even more. Thats the rods working for ya.
Being an amautuer astronomer, its not uncommon to see me running around the house in the early evening wearing an eyepatch with pantyhose stapled in to block out all the light so when I go out to observe, I can actually see quite a bit more.
On a side note, the eyes is least sensitive to red, and that is the light you want to use if you want to try to keep any dark adaptation. Hence why during the night, the control room is lit in red light. Makes it easier to pick out tha targets
Hope that helps ya out
Derrek