I've seen black and red in photos, so it may have varied with individual boats or patrol groups. The manual for the PBR MK2 describes it as: Glidden Co. Anti-Fouling Coat; Code NOGL-4637; FSN 1H8010-022-7969. The manual for the PCF MK2 indicates that 4637 is red.
Visit the Gamewardens of Viet Nam website (www.tf116.org) and see what they have to say.
Al