Colour replacement from 25I-NBOH

Colour replacement is a visual effect in which the perceived colors of objects, surfaces, or the entire visual field are substituted with colors that differ from their actual appearance. Unlike colour shifting (where hues continuously cycle through different values in a fluid, animated manner), colour replacement producesstatic, persistent changes — a green object becomes red and stays red, or the entire world acquires a purple tint that remains constant for the duration of the effect. The replacement holds steady, as though someone has applied a permanent color filter to reality.

The effect can manifest in two primary forms. In localized colour replacement, specific objects or regions of the visual field have their colors individually substituted. A tree's leaves might appear vivid red instead of green while the sky behind them remains correctly blue. A person's skin might take on an unnatural hue while their clothing appears normal. These selective replacements create a surreal, Photoshop-like quality to the visual environment, where parts of reality look correct while others are chromatically wrong in obvious and striking ways.

In global colour replacement, the entire visual field acquires a uniform color tint or cast. Everything might appear bathed in purple light, or the world might shift toward a warm amber, or the entire visual palette might undergo a wholesale hue rotation as though the color wheel of perception has been turned by some fixed number of degrees. This variant is less commonly reported but is particularly striking when it occurs, as it transforms the entire aesthetic character of the visual environment in a single, comprehensive shift.

Colour replacement reflects a disruption in the normal mapping between spectral wavelength processing andperceived color in the visual cortex. The eyes are still receiving the same wavelengths of light, but the brain's interpretation of those wavelengths has been altered at some point in the processing pipeline — likely in the color-selective areas of V4 and associated cortical regions. This is fundamentally a remapping error rather than a loss of color information (as in colour suppression) or an intensification (as in colour enhancement).

The effect is most commonly induced by moderate doses of psychedelics such as LSD, psilocybin, and mescaline, and it often co-occurs withcolour enhancement andcolour shifting. It tends to be intermittent and somewhat unpredictable in its specific manifestation — which colors replace which may vary from moment to moment or from one experience to the next.