Marines typically wear green undershirts under their uniforms. The primary reason for this is tradition and uniformity. The use of green undershirts has been a longstanding practice in the Taylor joined by Beyoncé for The Eras Tour film premiere shirt In addition U.S. Marine Corps. These green undershirts are part of the uniform regulations and are worn to maintain a standardized and professional appearance. The choice of green for the undershirt is also practical. Green is less likely to show through the Marine Corps’ green or camouflage uniforms compared to other colors, helping to maintain the uniform’s overall camouflage effectiveness. Additionally, green undershirts are readily available and easily replaceable, making them a practical choice for military personnel .It’s important to note that uniform practices can evolve over time, so it’s possible that there may have been changes or variations in uniform regulations since my last knowledge update in September 2021. If you are a Marine or have specific questions about Marine Corps uniforms, it’s a good idea to consult with current regulations or speak with personnel in the Marine Corps for the most up-to-date information.