I went to the Mayo Clinic's website. Here is what they say about dark brown or tea-colored urine with the following medical conditions:
Medical conditions. Some liver disorders, especially hepatitis and cirrhosis, and the rare hereditary disease tyrosinemia can turn urine dark brown. So can acute glomerulonephritis, a kidney disease that interferes with the kidney's ability to remove excess fluid and waste.
The only person who can really diagnosis your dad would be a medical doctor. Hopefully you can convince him he needs to see one.
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