Tip 1) Get someone to hold onto him really tight while you do it.
I'm kidding, but the question of how to paint a black dog is one that is often asked. They are tricky to photograph and paint. It can be hard to actually see them in the picture. The best pictures of black dogs make good use of lighting to highlight the form and expression.
I painted this short demo video to share with you. It shows one way to paint a black dog against a dark background, using oil paints. The surface I am painting on is primed fine linen on board 20x30cm
Mixing the colours
I dont use a tube of black paint for the colour of the dog and/or background. I do have some useful darks such as Asphaltum, Chromatic Black and Perylene Black, but I usually mix a dark colour from a combination such as Ultramarine and Burnt Sienna, or Magenta and Viridian. I always think a mixed colourful dark looks lively and interesting, as opposed to using too much black squeezed from a tube.
Once my darkest colour is mixed, i put it at one end of my glass palette, and I mix gradients of it in a range of values to use in my painting. I might mix two or three dark shades and then draw them out in this way. I mix white with a really tiny bit of the main colour for my lightest shade, so that it doesn't look too harsh/chalky.
Bear in mind that a photo reference will often bleach out the lightest light colour to appear lighter than you want it. The shadows usually appear darker than in reality. Shadows on photos can also seem flat and one dimensional. Use varied hues in shadows to bring them to life.