A $10 bath mat from Australian retailer Aldi has the internet up in arms as users attempt to figure out if it is meant to be purple or grey.
The item in question was recently purchased by an Aussie woman who thought she had bought a "lovely light grey" rug set from the budget retailer.
• Mind-boggling optical illusion that tricks your eyes goes viral
• Can you spot the hidden animal in this optical illusion?
• Twitter baffled by optical illusion of girl standing in a park
• Bride's wedding dress optical illusion baffles internet
That was until she got home and placed it in her bathroom.
"Tonight my husband comes in and says why do I have purple bath mats in my bathroom," she captioned a side-by-side photo of the mat.
"Checked it out and the damn things are now purple! I swear I purchased a light grey bath mat set.
"So can anyone clarify if I'm completely crazy or if these mats change colour in natural vs artificial light?
"P.S. not happy at all with our definitely purple bath mats."
The woman's post generated a flurry of comments, with many saying the mat was without a doubt purple.
One person took to the thread to share a photo of the mat taken on their lawn in full sunlight, before emphatically declaring: "I don't know how people can look at this and say it's grey?
"This is the same mat."
While another added: "Yeah, I saw them in-store and thought they looked purple so I didn't buy them as I wanted grey, I was disappointed."
A third, who also shared a photo, said they had bought the same set and could confirm it was "definitely grey in the store".
"But here it is against my light grey tiles.
Another said when they bought the mat it looked grey in-store and in the car on the way home, but purple in the bathroom.
"It looked a light purple in the bathroom but grey in the shop, car, lounge room before putting it in the bathroom.
"But it's the same colour as the set I got last year and never noticed it looked weird in the bathroom lol."
Others commenting said the mat appeared to be an "optical illusion where the eyes and brain ultimately perceive one colour and then we see a different colour moments later."
While another cited the internet sensation of 2015, commonly known as "The Dress".
"This is the blue/gold dress all over again. I see grey!" they wrote.
Digging into the science of optical illusions reveals that shifting colours have more to do with how the brain tries to register colour in terms of lighting.
According to The Independent: "When your brain tries to figure out what colour something is, it essentially subtracts the lighting and background colours around it, or as the neuroscientist interviewed by Wired says, tries to 'discount the chromatic bias of the daylight axis.'
"This is why you can identify an apple as red whether you see it at noon or dusk."
Making things even more confusing, Aldi are currently selling six versions of the bath mat, including two which are similar shades.
"Our Microfibre 2 Piece Bath Mat Set was available in six different colours. Two of these colours were lilac grey and sliver grey." a spokesperson told news.com.au.
"We encourage the customer to contact our Customer Service Team."