Complex sentence: The blue/white version is the authorized summer uniform for officers and SNCOs, and is worn only when an officer or SNCO is not in a formation situation with NCOs and enlisted Marines, except for the Silent Drill Platoon or other formations authorized by the Commandant.
Split into simpler sentences: The blue/white version is now an authorized summer uniform for officers and SNCOs, worn only when an officer or SNCO is not in a formation situation with NCOs and enlisted Marines. Exceptions are the Silent Drill Platoon or other formations authorized by the Commandant.