Some people are adamant it's blue and white, others are convinced it's black and brown. Some even believe it's green and gold.
The huge difference in opinion is a product of how our eyes have evolved, and how we manage to figure out what colour things are when they're lit by sunlight.
The challenge for humans is trying to avoid seeing the colour of the light reflecting off an object, and just seeing the colour of the object itself.
This happens constantly in our brains, without us even noticing or having to think about it. When you see a white sheet of paper lit by the yellow evening sun, your brain needs to 'subtract' the yellowness and and just see the white of the paper.
This system is also found in cameras, and is called white balance - the camera's mechanisms decide what should be white in the image, and adjust the colours accordingly.
However, just like The Dress did last year, the jacket confuses this system. The unusual lighting of the image makes our brains try to get rid of different colours in the image.
Depending on where we see the image, the colour of the background of the page it's on, or the lighting conditions, each person can see different colours - and once they've seen a certain combination, it can be hard to see another.
Other explanations of The Dress could also apply to the jacket, however - some believe that we're each wired to see colours one way or another, based on the numbers of rod and cone cells in our eyes.
Rod cells are more sensitive to light and are used to identify shapes, but not colours. Cones are less light-sensitive, but better at seeing colour. Having more or less of each of these cells could have an effect on the colours you see in the picture.
In reality, the jacket is blue and white, but there's no real 'wrong' answer when it comes to the colours we see in the image - it all depends on unconscious processes in our brains and eyes.