Ending the second day of painting with some great progress. In just a short amount of time I was able to sketch and underpaint the hawksbill sea turtle, granting me the perspective needed to place the other subjects.
The underpainting not only helps with perspective, but also acts as a base for any colors laid on top. If no underpainting was performed, the green hue of the turtle would be more in the blue spectrum. This is largely due to how thin I like to apply the layers of oil paints when working on the canvas.
Underpainting can be performed to create shadows, shades, and highlights, depending on the colors used. I typically like to paint shadows as dark blue, shades as Cerulean blue, and highlights as white, yellow or orange.