Australian Rock Doves, also known as Feral Pigeons, are descended from the Rock Pigeon, found in Europe and Asia. Many plumage variants have been developed by selective breeding over the years and the most common colours of feral birds are a mixture of grey, black, white and brown, with purple and green sheens (http://www.birdsinbackyards.net/species/Columba-livia). I spotted  this one in Sydney’s Botanical Gardens keeping an eye on the tourists admiring the lake.