As Ed pointed out, day shapes ball/diamond/ball. the balls are red, and the diamond is white. This hoist is displayed by any underway vessel, which, for various reasons, is extremely limited in its ability to alter its course. Typically, a carrier during flight ops, vessels engaged in underway replenishment, vessels tending channel markers,or bouys, etc. Vessels engaged in these activities after dark, display three lights red,over white,over red. If underway refuelling/rearming is being conducted, there will also be a "Bravo" flag flying. Bravo is a solid red flag, and can be part of a message hoist, but when flown by itself, indicates the handling of hazardous materials, and means stand clear. There are, of course, several "other" meanings of the phrase "flying Bravo".