Red, blue, violet and green - a whole spectrum of colours regularly show up on urine tests in hospital labs.
A scientist from Tacoma General Hospital in Washington has snapped a picture of a pee rainbow, a collection captured in just over a week of samples.
"My picture was intended to illustrate both the incredible and unexpected things the human body is capable of, the curiosity in science, and also the beauty that can be found in unexpected places," Heather West told the website, Live Science.
"A mix between art and science."
West said none of the samples were tested to change their colour.
"When I posted the picture [on Flickr], people thought that we did something magical to it. They did not believe it was actually urine."
Here, Kirsten Greene, an assistant professor of urology at the University of California, explains the colourful urine to Live Science:
Blood is the most common cause of red urine, and is a definite health warning signal. "As a urologist, I'm always worried when people have red urine," Greene said. Bladder cancer, infections and kidney stones can all cause bleeding that shows up in urine, and all are worth a trip to the doctor.
More benignly, eating a lot of beets can turn your pee pink.
Dark-colored urine also points to health problems. Liver cancer can cause dark brown urine, containing excess bilirubin, a brownish pigment produced by the liver.
A drug called phenazopyridine (Pyridium) created the bright orange urine seen in West's photograph. It's a painkiller given to people with urinary tract infections, and converts pee into a Gatorade-like color.
Antibiotics often alter urine color to orange, Green said. People who eat enough carrots to turn their skin orange can have orange pee, too, she added.
Many people have seen the effects of dehydration on pee - a dark yellow- colored urine. Without enough water, a pigment called urochrome becomes more concentrated in urine.
On the other hand, in hospitals, some patients on intravenous fluids are so hydrated they produce nearly colorless urine, West said. The cloudy, yellow urine in West's picture was caused by an infection.
Green urine usually flows from dilution of blue urine, as in West's image. Occasionally, a urinary tract infection may trigger green pee.
The rarest of all on the pee rainbow, blue urine often comes from chemicals and drugs given to patients. The number one offender is a drug called methylene blue, used to treat carbon monoxide poisoning, and as a dye during surgery. It makes the blue and green urine seen in West's photograph.
Methylene blue was also a malaria treatment during World War II. Other medications that make blue urine include Viagra, indomethacin and propofol - the anesthetic drug infamously linked with Michael Jackson's death.
Genetic conditions that affect the breakdown of dietary nutrients can also cause blue urine. Even blue food dyes sometimes passes into pee.
Indigo and Violet
In this photo, the deep purple urine comes from a patient with kidney failure. "The dark black one is something that you usually see in kidney failure," West said. "Your kidneys should be filtering your blood and getting rid of your waste, and when you damage the kidneys, there's a lot more blood [in the urine]," she said.
Another violet venue: Patients with catheters can develop a rare complication called "purple urine bag syndrome," linked to a urinary tract infection and highly alkaline urine. A genetic condition called porphyria may also trigger deep purple pee.