In the video above, you will focus the central white circle. Then, the image will change, and you will continue to fix the central point. What do you observe?
The second image appeared colored to you. In reality, it is black and white. But your eye, which stared at the first image full of color, gave you the impression that the next image was also colored.
This illusion is what we call an afterimage. It means that the previous image continues to exist in your brain even though it is no longer in front of you. This stored image is superimposed on the current black and white image. That is why you see it in color.