Yes, green dogs are real but they are, as expected, extremely rare. A puppy was born with green fur on a Sardinian farm very recently. They named him Pistachio after the green nut. The tiny dog was one of a litter of five belonging to a farmer whose name is Cristian Malloci. Green dogs occur when pale coloured puppies in the womb come into contact with the biliverdin pigment which causes bruises to be green. The rather beautiful pastel green shade will fade as Pistachio grows up.
At the moment I don’t know, and we are not told, how or why this pigment ended up in the womb of Pistachio’s mother. She may have been ill with an excess biliverdin pigment inside her circulatory system some of which leached into the womb. Another unanswered question is why this single dog was affected and not some or all of the others.
The biliverdin pigment is a “green tetrapyrrolic bile pigment, and the product of heme catabolism” (Wikpedia). As mentioned, sometimes bruises turn green but when biliverdin breaks down it turns into bilirubin which is yellow. That’s why you see yellow bruises after a while. People suffering from hepatic diseases have been found to have an excess of biliverdin in their blood. Jaundice is caused by an excess of this pigment or bilirubin (or both) in the circulatory system and tissues of people with this condition. Jaundice is caused by liver failure which in turn can be caused by excess alcohol over a long period.
Malloci has said that he will keep Pistachio and train him to look after sheep. His littermates will be given away to new homes. He adds that the colour green is a symbol of hope and luck and that his dog might bring a bit of joy to people during these difficult times with the coronavirus pandemic.