To technically clarify things a bit ... there is no 'right' or 'left' side to an aircraft or sailing ship. The terminology is 'port' and 'starboard', and bears great significance due to the designation being reference to a given side's orientation to the datum line's (commonly called centerline) forward direction. In a plan (top) view where the centerline is in the positive moment of the X axis, port would be viewed on the upper (positive) moment of Y, and starboard would be in the lower (negative) moment of Y. This becomes critical when viewing an aircraft from a distance - is it appraoching me?

For wing lighting designatiors, green is starboard and red is port. The aft (tail) end is marked with a white light. In the air or on the ground at night, it is always possible to determine the movement direction of the plane/ship based on knowing the coloring scheme of the lights. If it was merely left/right as stated in earlier posts, there would be absolute confusion when determining craft movement.

For manufacturing and maintenence, port/starboard is also a key technical reference. So to be concise: The flag is in standard orientation on the port side, and reversed on the starboard side.

GMF