The retina is the back part of the eye that contains the cells that respond to light. These specialized cells are called photoreceptors . The rods are most sensitive to light and dark changes, shape and movement and only contain one type of light-sensitive pigment. Rods are not good for color vision.
Rods are more numerous than cones in the periphery of the retina.
There are about 120 million rods in the human retina. The cones are not as sensitive to light as the rods. Signals from the cones are sent to the brain which then translates these messages into the perception of color. However, cones only work in bright light. That's why you cannot see color very well in dark places.