Try this simple visual experiment at home.

Create a dark room by turning off the lights at night. You’ll likely have appliances with small indicator lights of various colors. For example, last night in a hotel, the smoke detector on the ceiling had a flashing red light.

After your eyes adjust to the darkness, look directly at the small light. Then, gradually shift your gaze away and observe the light with your peripheral vision until it appears white.

This happens because the retina has two types of photoreceptor cells: cone cells and rod cells. Cone cells detect color and are concentrated in the fovea centralis, affecting your central vision. Rod cells detect light intensity but not color, and are more prevalent in the periphery, influencing your peripheral vision. In the dark, as the light moves out of your central field of view, you lose the ability to distinguish its color.

Here’s a second part to the experiment. Look directly at the small light and squint. The light will eventually appear white. During this process, you’ll notice an intermediate stage where the color is ambiguous.

This is because cone cell activity is light-dependent. Squinting reduces the luminous flux reaching the retina. In a dark environment, cone cell activity decreases. When the light becomes sufficiently dim, rod cells take over completely. At this point, your vision is similar to someone with total color blindness, and you can no longer perceive color.