It's short for "Federal Standard". These are paint color "standards" adopted by the Federal Government for paints authorized for military equipment. The number at the beginning indicates whether the paint is a flat, satin, or glosss. 3 designates a flat, 2 a satin, and 1 a gloss color. So 11136 would be gloss insignia red, while 31136 would be the flat variety of the same color.
Gip Winecoff