Union; 18th Massachusetts Volunteer Infantry wearing the full French Chasseur uniform .French Chasseur uniforms (10,000 sets were bought by the U.S. government) were issued to 3 regiments and possibly several others later on. Although well made many of the uniforms were too small for the whole lot to be issued. Most were returned to storage by the units , however some parts like the fatigue jackets and accoutrements were kept and used as late as the Gettysburg campaign.
Here is an older study of a member of the Zouave company of the 41st New York Volunteers (German volunteers) , the DeKalb Regiment. The only surviving jacket from this unit is in the vast Smithsonian collection and was used as the reference for this figure.