This propaganda is like all other propaganda's back then. It is trying to get people to join the Navy, in this sense. The image is saying that you are going to be on a gunship, loading the cannons and that it takes muscle to do that job. The colors help portray how it will look like. Since this was in the 40s, color helped bring in the audience more, and they didn't have TVs back then, or at least ones with color.
