What color is this dress?

Choose your answer wisely.

Everywhere you look, people seem to be debating an all-important question that has taken over Twitter and the Internet: What color is this dress?

Some see white and gold. Others see blue and black. There’s no middle ground.

The Great Dress Debate of 2015 began when a woman posted a picture of the polarizing garment to Tumblr and asked for help in identifying its colors. The dispute quickly spread Thursday night to Twitter, where people split into two camps: #teamblueandblack and #teamwhiteandgold.

Even Philadelphia police weighed in, tweeting: “WANTED: This dress to stop appearing in our feed (Even though we’d look simply ravishing in it) #BlueAndBlack.”

By Friday, everyone seemed to have an opinion on #TheDress.

Now, before you get in a fistfight and turn someone’s arm black and blue, let’s settle the crucial question: The dress is black and blue. The company that makes it has confirmed its color scheme.

We can blame the Internet for trolling our collective retinas. But science plays a role as well.

“It has to do with the tiny cones in the back of our eyeballs that perceive colors in a slightly different way depending upon our genes,” explains CNN’s Senior Medical Correspondent Elizabeth Cohen.

“The cones in our retinas — the fine layer of nerve tissue that lines the back of our eyes — detect the blue, green, and red in an image. The cones and your brain mix those colors to make other colors.”

Is the cat going up or down the stairs? People on social media are debating which way the cat is walking. Depends on how you look at it, right? Here are some other optical illusions that can trick the eye.

This dress became a viral sensation as people debated online about whether its colors were blue and black or white and gold.

The squares marked A and B are actually the same shade, as shown in the illustration on the right.

As you scan over this image, do you see gray or black dots? It's called a scintillating grid illusion, made by superimposing white discs on the intersections of gray bars against a black background. Dark dots seem to appear and disappear rapidly at the intersections, although if you stare directly at a single intersection, the dark dot does not appear.

The center of this image, made only with squares, appears to bulge out, even though all of the lines are actually straight.

If you move your head while staring at these circles, they will appear to rotate or spin. But that movement is only an illusion.

Same with these circles. Move your head around while staring at them, then hold your head still. The circles will appear to rotate briefly.

More optical illusions like #UporDown

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CNN’s Sarah LeTrent contributed to this story.