Colour suppression from PCP

Colour suppression is the visual experience of colors becoming duller, darker, and less distinguishable from one another. Reds lose their warmth, greens fade toward grey, blues wash out, and the overall chromatic richness of the visual environment is steadily drained. The world takes on an increasingly desaturated, washed-out appearance — as though someone is slowly turning down the saturation slider on reality itself.

At lower intensities, the effect is subtle enough that it might not be consciously identified as a distinct phenomenon. Colors simply seem "less vivid" than usual, and the environment may feel slightly flat or lifeless without the observer being able to pinpoint exactly why. At moderate intensities, the desaturation becomes obvious: distinct hues blur into one another, color contrasts weaken, and the visual world takes on a distinctly grey, muted quality. At its highest levels, colour suppression can render the entire visual field effectively black and white — a complete monochrome experience in which all chromatic information has been stripped away, leaving only luminance values (light and dark) intact.

The phenomenology of this effect is essentially the inverse of colour enhancement, and the two exist on opposite ends of the same perceptual spectrum. While psychedelics typically push color perception toward the enhancement end (more vivid, more saturated, more luminous), substances that suppress neural excitability — particularlyantipsychotics — tend to push it toward suppression. This makes pharmacological sense: colour enhancement appears to result from increased gain and responsiveness in color-processing circuits of the visual cortex, while colour suppression reflects a dampening of these same circuits.

Colour suppression is most commonly associated with antipsychotic medications such as quetiapine, haloperidol, and risperidone, where it often co-occurs with other suppressive visual effects includingacuity suppression (reduced visual sharpness) anddouble vision. It can also occur during the comedown phases of stimulants, during depressive states, and with heavy doses of certain sedating substances. While not dangerous in itself, the perceptual flattening produced by colour suppression can contribute to feelings of emotional blunting, anhedonia, and disconnection from the environment.