This is the cap issued to all troops by the US Army during WWII. They are made from the same type of wool serge as the Service Coat and Wool Trousers.
Branch of Service Piping: Once a soldier was assigned to a unit, colored trim was usually sewn around the lip of the cap fold. (A few soldier's did not get this done for one reason or another, especially in the middle of the War.) These are stocked with blue (infantry) piping or no piping at all. For all colors other than blue, there is a $14.99 charge to partially dis-assemble the cap to sew in the desired color of piping. "No piping" is still considered "custom" but there is no upcharge.
Colors other than Infantry blue = "Custom Piping" since we have to add it to the cap. Piping and sewing cost $14.99 and may entail a shipping delay of 2-5 business days depending on the workload in the factory.
1st Special Service Force- red/white/blue
Air Corps- yellow/blue
Warrant Officer- silver/black