The colors blue and green are common in nature and widely used in human culture. But are there situations where these colors seem to disappear from view? This article explores when and why blue and green may go unseen.
The Physics of Color Perception
To understand when blue and green are not perceived, we first need to review some basics of color and vision. The visible spectrum encompasses light with wavelengths from about 400 to 700 nanometers. Blue light has wavelengths around 450-495 nm, while green wavelengths are 495-570 nm.
Our eyes contain cone photoreceptor cells that are sensitive to different wavelengths of light. There are three types of cones:
- S cones – sensitive to short wavelengths (blue)
- M cones – sensitive to medium wavelengths (green)
- L cones – sensitive to long wavelengths (red)
When light hits the retina, the cones are stimulated to different degrees depending on the wavelengths. The brain interprets the cone signals as color. For us to see blue or green, the S and M cones need to be sufficiently stimulated.
Low Light Conditions
One situation where blue and green are not perceived is in very low light. In darkness or near-darkness, there is not enough light energy to strongly stimulate the cone cells.
Rod photoreceptors take over vision in low light. But rods do not detect color – they only register shades of gray. So in very dim conditions, everything appears colorless. This is why colors seem to disappear or fade to gray at night.
Color Deficiencies
People with certain visual impairments may also have trouble perceiving blue and green. The most common deficiency is red-green color blindness, where the M cones are abnormal. This makes it difficult to distinguish some shades of red, green, brown, and orange.
Less common is blue-yellow color blindness, involving the S cones. Without functioning S cones, blues will appear greener and yellows will appear pinkish. Complete color blindness (monochromacy) is very rare, but means only shades of gray are seen – no colors at all.
| Type | Cone Deficiency | Effects on Color Vision |
|---|---|---|
| Red-green deficiency | M cones abnormal | Reds, greens hard to distinguish |
| Blue-yellow deficiency | S cones abnormal | Blues look greener, yellows pinkish |
| Complete color blindness | All cones nonfunctional | Only see shades of gray |
So for people with blue-yellow deficiencies, blue and green hues may be largely imperceptible.
Interaction with Other Colors
Context also affects color perception. Visual illusions can make a color seem to disappear or change when surrounded by other colors.
For example, in the Pinna illusion below, the inner green squares appear brighter at the intersection with the blue. Where green overlaps purple, the green looks darker. The same green color is objectively present, but seems subjectively altered by the color interactions.
Carefully designed patterns of color contrast can visually trick the eyes and brain. So blue and green may not be perceived in certain contexts due to optical illusions.
Screen Technologies
Displays like televisions, phones, and monitors use different methods to create color. Some technologies inherently have trouble reproducing blues and greens accurately.
Older CRT screens used phosphor to emit red, green and blue light. But the blue phosphor declined in brightness over time, causing blue hues to look dim and greenish.
LED and LCD screens use liquid crystals and RGB filters. But some screens may not have enough resolution or calibration to render subtle shades of blue/green well. Compression artifacts in video streaming can also distort color.
Poor color reproduction can make blue/green hard to distinguish. But display technology keeps improving, so this issue is diminishing.
Background Effects
The background against which colors are viewed also influences perception. This is called simultaneous color contrast. A color may appear different depending on the surrounding colors due to adaptation effects in the eyes.
For example, a neutral gray patch looks slightly greenish on a red background and slightly pinkish on green. A blue patch can look darker and less vibrant when viewed against a saturated orange background.
So in some settings, blue and green colors may perceptually shift toward other hues or lose brightness/saturation. The effect is not extremely dramatic, but can contribute to blue and green blending into the background.
Age-Related Changes
As people age, visual changes occur that can affect color perception. The lenses in the eyes gradually yellow, filtering out some blue light. The cornea also yellows and becomes less transparent. With less blue light reaching the retina, blues are perceived as greener or grayer.
The cones also gradually deteriorate with age. Density of the S cones detecting blue light decreases more rapidly than other cones. This age-related loss of S cones can make distinguishing blues from greens more difficult.
So elderly people may perceive fewer color differences in the blue/green range. However, the shifts are usually subtle and vision remains adequate for everyday function.
Extreme Conditions
There are some extreme environments that preclude seeing blue or green. For example, at very high altitudes, shorter blue wavelengths are scattered out of sunlight by the thin air. This gives a dominance of yellows and reds – explaining the vivid sunsets viewed from mountains.
Underwater, the longest red wavelengths are absorbed first by the water. At deeper depths, eventually all colors drop out except for blue. Everything appears blue or colorless underwater without artificial light.
In outer space, the lack of atmosphere and daylight causes colors to appear totally black. Astronauts on the Moon reported it as colorless, like being inside a lightbulb. So in these exotic situations, blue and green effectively disappear.
Conclusion
While blue and green are commonplace colors, our perception of them can change or vanish entirely depending on the conditions. Low light, visual impairments, surrounding colors, display technologies, age, and extreme environments all play a role. But thanks to the complexity of human color vision, blue and green are abundant parts of the visual experience for most people in everyday life.
