A dress that some people see as being blue-and-black and some see as white-and-gold has captured everyone’s imagination this morning. Here’s how to tell what colour it actually is, using Photoshop.

 A photo of a dress has polarised people across the Internet (and in the Digital Arts office). Looking at the photo below by Tumblr user swiked, some people see it as being blue-and-black. Others see it as gold and white. Neither can understand why the other sees it so differently. Arguments have ensued – online at least, we’re far too civilised to starting shout at each other about what colours it is (honest).

Wired has done a great job of explaining the science behind why you might see it differently from I – essentially your brain automatically discards what it thinks is a colour cast caused by the colour of the light in a place, like a neurological version of Photoshop’s Auto Color feature. So for fun I thought I’d try to use Photoshop to answer the question of what colour the dress is once and for all.

Opening the photo in Photoshop, I used the Color Picker on some randomly chosen parts of the dress to see what it is.

First off, the lighter area of the dress.

With RGB values of 124/135/167, 98/103/127 and 132/152/189 the lighter area of the dress is definitely between blue, gray and purple. Here they are on their own.

The darker area’s RGB values varies from 130/113/73 to 88/73/39 – yellowy browns that could conceivable be described as representing gold.

Again, here they are on their own.

However, the colour of the light and that most artificial lights in shops has a yellow hue means that you could assume that this is yellow light falling on a black dress. But unlike whether it’s blue or white, that’s an conscious decision, not a subconscious adjustment in your brain.

So the dress is either blue-and-gold/brown or blue-and-black. It’s definitely not white.

Though as that Wired article shows, it doesn’t matter who’s right – it’s what this tells us about how our eyes and brain work that’s truly fascinating.