The color of our urine is a kind of “health indicator” that reflects what’s happening inside the body. A change in its shade can be caused by harmless reasons, such as dehydration or eating certain foods.

However, in some cases, an unusual urine color may be the first—and sometimes the only—warning sign of serious diseases, including cancer. In this article, we’ll look at three key urine colors that can point to cancers of the urinary system and explain why it’s so important to see a doctor immediately if they appear.

As a urologic oncologist with over 20 years of clinical experience, I see patients every day who waited too long to seek help because they ignored these warning signs. This article is a detailed guide based on both clinical practice and modern medical research.

Color #1: Red or pink — blood in the urine (hematuria)

Hematuria is the presence of blood in the urine. It’s the most alarming and obvious symptom, and one that must never be ignored. A red or pink tint may be caused by a small amount of blood or by a significant amount.

Why it’s concerning: Blood in the urine can result from inflammation (such as cystitis or pyelonephritis), injury, or kidney stones. But the most dangerous cause is bladder cancer or kidney cancer. As a tumor grows, it can damage blood vessels, leading to bleeding.

Cancer-related hematuria has several distinct features:

Painless. Unlike blood in the urine from stones or infection—which often comes with painful urination, burning, or cramping—hematuria caused by cancer is usually painless. This makes it especially dangerous and deceptive.

Intermittent. Blood may appear and then disappear, giving a false sense of improvement. Patients often think the problem has gone away, so they don’t see a doctor. In reality, the tumor may have just temporarily stopped bleeding.

Visible or hidden. Blood may be visible to the naked eye (gross hematuria) or detectable only under a microscope during a urine test (microscopic hematuria). Either way, it’s a red flag that requires a thorough evaluation.

Color #2: Dark brown or black — breakdown products

Dark brown or even black urine is a very rare but very serious symptom. It can be triggered by harmless or highly dangerous causes.

Harmless causes: Eating beans, rhubarb, or aloe. Certain medications can also darken urine.

Dangerous causes:

Melanoma. Malignant melanoma (skin cancer) can spread to internal organs, including the kidneys. Tumor breakdown products may be excreted in the urine, turning it dark. This signals metastasis and is extremely concerning.

Kidney cancer. Some kidney tumors can cause muscle tissue breakdown, releasing myoglobin, which stains urine a dark brown color.