What colour are these spheres? Most people are tricked by this uncanny optical illusion - how it works

An optical illusion that baffles and tricks the brain has gone viral on Twitter.

For many people, the image appears to contain 12 colourful spheres.

It might be on the older side but it still can bamboozle your mind.

On first glance at the picture, it appears as if the sphere are one of three colours - pink, blue and green.

However, not everything is what it seems!

What colours are the spheres?

Have you taken a look at the image yet?

It probably appears as if you are looking at 12 colourful spheres, with a number of coloured lines cutting through them.

The colours will probably look pink, blue and green to many viewers.

However the spheres are actually brown!

One person wrote: “I’m confunded.”

Another responded: “Ok, that got me for a minute I’m not ashamed to admit! Cool illusion.”

One user reacted: “This is witchcraft.”

Another added: “And the skies are grey.”

However, a number of people were actually able to see the spheres as brown to begin with.

One wrote: “What… are they supposed to look like? Of course they’re brown? They look brown?”

Another added: “Yes, they are. Guess these optical illusions don’t work on me.”

How does the illusion work?

It is important to remember that perception is not always reality.

The image comes from David Novick, who is a Professor of Engineering Education and Leadership, the University of Texas at El Paso.

In it the spheres are floating behind a series of red, blue and green lines.

And it is these lines which cause the spheres to appear as if they are colourful - not brown.

David Novick tweeted: “A three-color confetti illusion with spheres, which appear to be yellowish, reddish, and purpleish but in fact have exactly the same light-brown base color (RGB 255,188,144). Shrinking the image increases the effect.”

In another twist, depending on where your eyes are focusing on the image the colours of the spheres can change.

For example a “purplish” sphere may appear reddish or greenish.

How can you see the brown spheres?

If you remove the red, green and blue lines which streak sideways across the image, then the spheres will be clearly brown.

Responding to a reply, where the user had stripped back the coloured streaks, David Novick said: “Very nice! This neatly matches the original with the foreground stripes removed.”

What causes your brain to see the colours?

The optical illusion works by creating a disconnect between the raw data taken in by our brain and the way that information is processed.

When our eyes perceive colours, they also take into account the colours surrounding it.

So in this case, because of the streaks cutting through the spheres, our brains are perceiving the red, blue and green as well as the brown.

It is an example of the Munker–White’s illusion.

Novick told LiveScience the illusion works because: “our acuity for shape is better than our acuity for color, which means that we perceive the shapes with more detail and the colors with less detail”.