Short answer
Fog droplets scatter all wavelengths almost equally, adding white light between you and everything you look at, so contrast and saturation collapse with distance. In clear air, the air itself scatters blue light into the line of sight, so distant dark hills take on a blue veil — aerial perspective. Haze made of finer particles sits between the two and can tint the veil.
When you look at a distant object, two kinds of light reach you: light from the object, weakened along the path, and light from the sun or sky scattered into your line of sight by whatever the air contains. The second, the veiling or 'airlight', is added to every distant thing regardless of its own colour. As distance grows, the object's own light fades and the veil grows, until the object is indistinguishable from the sky. Painters have exploited this for centuries as aerial perspective: fainter, lower-contrast and bluer means further away.
Fog is a cloud at ground level: water droplets comparable to or larger than light's wavelength. Like cloud, it scatters by Mie scattering, nearly equally at all visible wavelengths, so its veil is white. Colours do not shift towards any hue in fog; they desaturate and lighten towards white, and dark colours lose the most because the added white is a larger fraction of what reaches you from them. Headlights and streetlights produce glowing halos for the same reason, since light is scattered forward around the source.
In very clean air the veil comes mainly from molecules, which scatter blue preferentially, so distant forests and ridges turn blue and the more distant ranges bluer still. Haze particles — sulphates, sea salt, organic aerosols, smoke — are intermediate in size; they scatter more strongly than air and less selectively, whitening the blue. Some pollution haze absorbs as well as scatters, and can give distant views a yellow or brown cast rather than a blue one. The colour of distance is therefore a rough indicator of air quality.
Fog and haze are low-contrast rather than coloured conditions. For signs, safety markings and vehicle lights, the question is whether an object's contrast with its background survives the added veil, which is why high luminance contrast matters more than hue in poor visibility. For judging colour, anything more than a short distance away in fog or haze is not showing its own colour at all. For photographs, dehaze tools work by estimating and subtracting the airlight; they recover contrast but can only guess at the true colours.
Why: Veiling light swamps low-reflectance surfaces first.
Fix: Rely on luminance contrast rather than hue for anything that must be visible in fog.
Why: Airlight adds a blue or white veil that the eye partly discounts but the camera records.
Fix: Use a polariser in clear conditions, shoot closer, or apply dehazing with care.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
Water droplets are much larger than air molecules and scatter visible light almost independently of wavelength, producing white glare rather than blue.
Source: HyperPhysics (optics, atmospheric optics and vision pages)
FactStrong evidence
Scattering by air molecules favours short wavelengths, so light scattered into a clear-air line of sight is bluish.
Source: HyperPhysics (optics, atmospheric optics and vision pages); The Color of Clouds (JetStream)
Colourwise interpretationModerate evidence
In fog, dark colours lose visibility faster than light ones, because the added white veil is a larger fraction of the light reaching the eye from a dark surface.
Based on: Follows from adding a constant wavelength-neutral veiling luminance to object luminances of different sizes; a contrast argument, not a field measurement.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.