Soulen's style included bright colors, limited depth, and cloisonnist outlining of his subject matter. These traits are commonly found in murals painted in the late 19th and early 20th centuries.
Here is an example of a problem faced by me and other bloggers who make use of unfamiliar images found on the Internet. Not having seen the original art or even a printed reproduction, I have no sure way of telling what the original coloration was like. Above are two versions of "The Parade." The upper version has more naturalistic colors. But I wonder if the image was scanned from a magazine; illustration colors were and are altered purposefully or otherwise during the publication process. The lower version has better resolution (you can see more impasto brushwork: click to enlarge), yet the colors don't strike me as realistic for a German scene. If any reader knows for certain what the original colors were, please post a comment.