When Purple Perceived Only at Fixation: A Fixation and Distance-Dependent Color Illusion

Are these dots purple or blue?

Here are two optical illusion, wherein purple structures are perceived as purple exclusively at the point of fixation, while the surrounding dots transition towards a blue hue. As the viewing distance increases, a greater number of dots revert to a purple appearance, culminating in the pattern being perceived as uniformly purple.

9 Purple Dots Illusion — **9 Purple Dots** Move your gaze from one to another dot. The one you are focusing on appears purple while the other perceived more blue. (c) H. Schulz-Hildebrandt

Color Changing Dots Illusion — **Color Changing Dots** When changing the distance to the monitor, more or less dots perceived as purple. (c) H. Schulz-Hildebrandt

This effect is best visible on a cellphone display. It will be less obviously when the color temperature of the display has changed (NightMode, Dark mode etc.)

Ho does this (likely) works?

First, a classic color contrast effect, which would explain why the periphery structures show up in blueish, second, the reception of purple as a non-spectral color that is created exclusively through the combinet stimulation of red and blue receptors, and third, the biological distribution of the light receptors, especially the absence of blue receptors in the center of the fovea. The combination of these three effects aligns with the perception of the optical illusion which only occurs reliably in a narrowly limited color space and is clearly dependent on the viewing distance.

More details: Color Changing Dots Illusion