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This is quite an interesting effect because, unlike a simple afterimage, this one lasts a long time. As with all our services, by using this site, you agree to the Terms of Service.
The McCollough effect is a phenomenon of human visual perception in which colorless gratings appear colored contingent on the orientation of the gratings. It is an aftereffect requiring a period of induction to produce it. For example, if someone alternately looks at a red horizontal grating and a green vertical grating for a few minutes, a black-and-white horizontal grating will then look greenish and a black-and-white vertical grating will then look pinkish. The effect is remarkable because, although it diminishes rapidly with repeated testing, it has been reported to last up to 2.8 months when exposure to testing is limited.
The effect was discovered by American psychologist Celeste McCollough in 1965.
Easily experience this effect yourself with this simple test! Read the instructions before you begin. Also, make sure your browser is not significantly changing the color scheme of this page (e.g. from a force dark mode feature, from a night mode/warm color shift feature, etc.).