ColorAssim
Color Assimilation Illusion
Free
See yourself in a new color. ColorAssim uses a 150-year-old illusion to tint your face with every color of the rainbow — no filters, just perception.
Color assimilation was first described by Wilhelm von Bezold 150 years ago: when thin colored stripes are overlaid on an image, the colors of the image appear to shift toward the stripe colors. With time, these illusions have become increasingly dramatic — from the classic Bezold spreading effect to the Munker illusion, the Monnier-Shevell illusion, and most recently the Confetti illusion by David Novick.
We find that color assimilation works particularly well with human faces. ColorAssim lets you experience this directly: take a selfie or a portrait, and the app automatically segments your face and renders it nine ways — across three color sets (RGB, black-gray-white, and CMY) and three stripe phases. Watch the same face appear red, green, blue, yellow, cyan, and magenta, all at once, just by changing the color of the overlaid stripes.
The effect is not a filter. Your face hasn't changed — only your perception of it has. Don't believe it? Tap the image, and the stripes covering the face fade away to reveal the unchanged colors underneath. Pinch to zoom in on the very pixels: they stay identical while the illusion comes and goes. Tap again, and the colors snap back.
Share the result or save it to your photo library — with or without the stripes. And the little "?" button explains the science behind the effect.
Learn more about the illusion, with demos and background: https://www.allpsych.uni-giessen.de/karl/ColorAssim/
Based on research published in iPerception (2024): https://doi.org/10.1177/20416695241258748
PS: Works with your pet, too. Just use the oval region when the segmentation gives a warning message!
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• Tap the result image to hide the stripes over the face — and see that the face colors never actually change
• Pinch to zoom in for a pixel-level look at the illusion
• New "?" button on every screen, linking to an explanation of the effect
The developer, Karl Gegenfurtner, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Karl Gegenfurtner
- Size
- 2.2 MB
- Category
- Education
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - iPad
Requires iPadOS 17.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- Copyright
- © 2026 Karl Gegenfurtner