Colour enhancement is a perceived intensification of the brightness and vividness of colours in the external environment. During this experience, reds may seem “redder”, greens may seem “greener", and all colours will likely appear much more distinct, complex, and visually intense than they comparatively would during everyday sober living.         At higher levels, this effect can sometimes result in seeing colours that are perceived as surreal or seemingly impossible.  
Colour enhancement is often accompanied by other coinciding effects such as visual acuity enhancement and increased pareidolia.   It is most commonly induced under the influence of mild dosages of psychedelic compounds, such as LSD, psilocybin, and mescaline. However, it can also occur to a lesser extent under the influence of certain stimulants and dissociatives such as MDMA, ketamine  , or 3-MeO-PCP.
- Gallimore, A. R. (2015). Restructuring consciousness–the psychedelic state in light of integrated information theory. Frontiers in human neuroscience, 9, 346. | https://dx.doi.org/10.3389%2Ffnhum.2015.00346
- Obreshkova, D., Kandilarov, I., Angelova, V. T., Iliev, Y., Atanasov, P., & Fotev, P. S. (2017). Pharmaco-toxicological aspects and analysis of phenylalkylamine and indolylalkylamine hallucinogens. Pharmacia, 64(1), 32-47. (2) | http://bsphs.org/wp-content/uploads/2017/04/Angelova.pdf
-  Bersani, F. S., Corazza, O., Albano, G., Valeriani, G., Santacroce, R., Bolzan Mariotti Posocco, F., ... & Schifano, F. (2014). 25C-NBOMe: preliminary data on pharmacology, psychoactive effects, and toxicity of a new potent and dangerous hallucinogenic drug. BioMed Research International, 2014. | https://dx.doi.org/10.1155%2F2014%2F734749
- Abraham, H. D. (1983). Visual phenomenology of the LSD flashback. Arch Gen Psychiatry, 40(8), 886-887. | https://jamanetwork.com/journals/jamapsychiatry/article-abstract/493119
- Baggott, M. J., Coyle, J. R., Erowid, E., Erowid, F., & Robertson, L. C. (2011). Abnormal visual experiences in individuals with histories of hallucinogen use: a Web-based questionnaire. Drug & Alcohol Dependence, 114(1), 63-64. | https://doi.org/10.1016/j.drugalcdep.2010.09.006
- Dillon, P., Copeland, J., & Jansen, K. (2003). Patterns of use and harms associated with non-medical ketamine use. Drug & Alcohol Dependence, 69(1), 26. | https://doi.org/10.1016/S0376-8716(02)00243-0