When painting a fire in Photoshop, it is important to use a light and dark color palette to create the desired effect. The colors should be used sparingly, as they will be used again and again in the final image. To start, choose a light color such as blue or green. Next, use a dark color such as black or navy to create the base of the fire. Add any additional colors you want to the flames by using different shades of black or white. To make the fire more realistic, you can add sparks and embers by using different types of brushes. You can also use filters to change the appearance of the flames.