How many colours do you see? Popular vision test debunked

Three months after social media went crazy about #TheDress and the mystery of why people see it in different colours, folks are still trying to figure out what the science behind this optical illusion is.

As many as 10 million tweets went out about the image of the horizontally-striped dress in just the first week of it appearing online. Was it black and blue or white and gold?

One particular explanation put forth by self-described neuromarketer and researcher Diana Derval that has making the rounds involves the number of classes photoreceptors or cones in the retina of the human eye - which can range from two to four. The more types of cones, the more of the colour spectrum that can be seen.

In this article Professor Derval showcases a spectrum of colours and asks readers to take an online test to see how many variations or shades of colour they can distinguish.

Try it: How many colours do you see?

According to the author,  about 25% of the population should be able see all the shades as they are presented thanks to having a fourth cone or being what’s called tetrachromatic.

“It is highly probable that people who have an additional 4th cone do not get tricked by blue/black or white/gold dresses, no matter the background light ,” stated the Derval in her article.

Meanwhile she goes on to point out that 50% of the population can see somewhere between 20 to 32 colour nuances making them trichromatic, while the remaining 25% see fewer than 20 shades and are classed as dichromates. This group would have only two types of cones making them similar to dogs in their colour recognition capabilities. And in terms of fashion sense the trichromatic would favour greens, blues and reds in their wardrobe choices while dichromate would be drawn to beige, black and white attire.

Does this sound like bunch of hooey? It may just be according to leading vision scientists.

It looks like Derval’s online colour test may have been debunked after all, adding to the colour controversy with people now perhaps falsely identifying themselves as tetrachromats, say vision scientists.

In the article the author estimates that about about a quarter of the population are tetrachromats however it turns out that the actual numbers may be a bit more interesting and skewed towards one sex.

“About 50% of  females and 0% of males have 4 cone types,” said vision expert and professor Stephen Dain, from University of New South Wales, Sydney, Australia.

“Whether this results in superior colour vision [however] is very much in doubt.”

He goes on to point out that rather than 25% of the population being  dichromats as stated in Derval’s article the numbers are actually much lower with only  2% of males and 0.002% of females having only two functional types of cones.

And while the questionable story claims that dichromats tend to wear back, beige, and blue, the fact is that  “dichromats may wear quite outlandish and clashing colours,” explained Dain.  

“Many wives will label their husband’s clothing for colour coordination.”

And what about colour-blindness? Research has shown that about less than 10 percent of men have it while only 0.5% of women. In this case two genes carried on the x-chrosmosome are to be blamed and are lacking in those that are colour blind. Because women have two X- chromosomes, there is a greater chance of just being a carrier, however in males there is only one X-chromosome and if it has the faulty genes, they are doomed to colour-blindness.

Most folks who suffer colour impairment - they tend not see shades of red and green.  Interestingly Facebook founder Mark Zuckerberg chose to go with blue for his web venture because it’s the ‘richest’ colour he can see.

And while normally colour-blindness involves having the deficiency to distinguish a few shades of a particular colour, there are the rare cases of total blindness to all colours. Known as achromatopsia - it affects only one every 33,000 people. And while its normally not fatal it can lead to tragedy as was the case with one individual with this rare condition who died in a car accident after having mistakenly run a flashing red light.

And while true tetrachromats are not as rare, having a fourth active cone can allow an individual to see 100 times more shades of colour than the rest of the world.  But in regards to that online colour test, the final nail in the coffin of its veracity, according to Dain, has to do with the limitation of our computer screens and digital devices.

“A computer can display 16.8 million colours, trichromats can see more than that, not 33-39 [as stated in the online test],” he added.

Follow Andrew Fazekas on Twitter: @thenightskyguy