Churchill talked of it. There is a rather good website devoted to it. It is an image which traditionally fits the feeling of depression lurking around. Black dogs and depression are inextricably linked. Which is a shame for black dogs and for my friends at Black Dog Media who seem very cheerful and do a great job.
So, how about introducing a white dog to the black. Let's imagine them meeting - a large black labrador and my favourite small white dog, a Westie. Particularly this one, Lulu, who has been a house guest here and a very cheery one. (That's David Beckham under her paw, who is about to be decimated.)
From now on I shall try to introduce Lulu when my black dog is looming. In fairness to black dogs, my low moods will be clouds from now on, not dogs. Except, being greeted by Lulu first thing in the morning can stand for a cherished moment when I experienced pure joy, to be held mindfully in a safe place.