Optical illusions show us how our brains work. Now, an image created by Japanese psychologist Akiyoshi Kitaoka is another lesson in our colour process. In one of his latest paintings, titled "Fantasy Yellow," you can see three overlapping circles in cyan, magenta, and yellow, just like you would see in a CMYK model representation. However, a closer look reveals that the bottom circle is not actually yellow. Colour is created in our minds.
So why do I see a yellow circle when it doesn't exist? The answer lies in subtractive colour mixing, or the perception of colour created by the absorption of light from other colours. If you zoom in on the image, you'll see that what you think is a yellow circle is actually a black line on a white background. These lines follow the same pattern as the normal image, but the other lines are blue.
The illusion of yellow is then created by black and white stripes in the area surrounded by blue stripes. Additionally, what corresponds to the green area where the blue and yellow meet is composed of cyan and black. To further prove this, Twitter user Mab Newemka said that you don't need to have two different colours for this illusion to occur. If you drag the circle from the black stripe to the blue stripe behind it, the yellow circle will appear almost perfectly.