Many color illusions are based on the simple fact that when judging the color of an object we are influenced by the color of its surroundings, as this very simple image vividly illustrates. The three blue discs are precisely the same shade of blue, but they look quite different when seen against different backgrounds.

As another example of the same phenomenon of color perception, there is only one shade of red used in this image, but putting the red squares adjacent to either green or white squares dramatically changes our perception of the color.

In one class of very strong illusions, overlaying grids or lines of different colors dramatically changes our perception of the color of the image ``behind" the grid. In this image, all the rings have the same basic color! [Thanks to Prof. Novick.]

In this amazing example, thanks to Prof. Kitaoka, there are no red pixels anywhere in the image, but since we know strawberries are red, our eye-brain system supplies the expected color.  Check this link: https://www.sciencealert.com/in-spite-of-what-your-eyes-tell-you-these-strawberries-aren-t-red