Note: the above is a museum display that shouldn't be used as a color reference.
On the TBD, the Mk 13 was carried externally. Operational pictures taken prior to the Midway torpedo attack disaster indicate that the warhead section was gray, probably the same color as the bottom of the TBD, while the rest of the body was brass colored.
By then, a wooden "box" had been developed to improve the ballistics of the torpedo so it entered the water cleanly and at the desired angle. The box would break off when the torpedo hit the water. Unlike the later tail box, it had scolloped sides with a square or rectangular top and bottom inclined at an angle to the longitudinal axis of the torpedo (the edge of the fins was not angled so it wasn't inclined for that reason).
This is a picture of a test of this box in October 1941. Note the scalloped side panels and the thickness of the upper and lower sides.
An extensive development and qualification program resulted in a very satisfactory weapon by 1944. The only external change to the torpedo itself was the ring tail, which improved the stability of the torpedo in the water so it ran straight at the set depth.
In addition, a new set of plywood appendages was added to improve the torpedo's stability in the air and eliminate damage when it hit the water. The wooden barrel on the nose was called the drag ring. It slowed the torpedo from the drop speed prior to water entry and also acted as a shock absorber. The plywood box on the tail was redesigned and simplified. Both of these wooden structures were designed to break away when the torpedo hit the water.
The later torpedoes may have had an olive drab warhead, the same as bombs, and a more silvery power unit.
The TBD's successor, the TBF/TBM Avenger, carried the torpedo in a bomb bay so the well-described drag ring was not a problem. The subsequent attack airplanes, the AD Skyraider and the AM Mauler, were to carry the torpedo externally. To reduce drag, a streamlined nose cap was developed that was pulled off by a lanyard when the torpedo was dropped.
However, the nose cap wasn't used for the last combat torpedo drop on the sluice gates at the Hwachon Dam during the Korean War.