Prepping the image
I like using flat coloured layers as another test for the colours and values. The great thing about this graphic version of the image is that I can use it later to grab selections of those different parts of the image. I just keep a stack of layers or a flatcoloured version under the image and then select them as necessary later.
Start the underpainting
Once I’m happy with the rough, I start with my background. I’ll sometimes begin with a colour that I wouldn’t mind showing through the cracks in the painting – in this case a bright orange that pushes the intensity of the scene where it peeks through the background. I paint enough of the background in to set the context for the characters.