This is really strange. First off, if it was liver function problems, there wouldn't be a debate . It would be obvious. Secondly, I've seen coloration changes, at length, in such patients. One can turn yellow, one can turn green if the liver is actually failing, but I haven't seen dark brown. I don't recall it being a symptom of hydroxychloroquine either, or any drug I can think of that someone with respiratory problems would be on.

What it looks like to me is a symptom that sometimes occurs with Addison's Disease, where one has adrenal insufficiency. It doesn't happen to all of them, but you can take on the color of negro skin, and / or get dark freckles. And they're not looking for adrenal probs with a respiratory illness. Another mystery, like the doc who said his "Coronavirus" patients look like those that suffered a lack of oxygen from high altitude exposure.

Zerohedge article

Dr. Yi Fan and Dr. Hu Weifeng both survived coronavirus after being infected while treating patients in the city of Wuhan, where they both worked. But after they were placed on life support, their skin turned "very dark".

Both doctors were diagnosed back in January while working at Wuhan's central hospital and were eventually taken to the Wuhan Pulmonary Hospital and transferred twice as a result of their serious condition.

While initially the change in their skin color was attributed to a hormonal imbalance after their livers had reportedly been damaged by the virus, another doctor suspected that it could have been as a result of one of the drugs they received during the beginning of their treatment, according to the NY Post. 

"When I first gained consciousness, especially after I got to know about my condition, I felt scared. I had nightmares often,” Dr. Yi said after spending 39 days on life support.