The Mk-13 torpedoes carried in the roll-off rack from mid to late '43 on had a number of warhead colors. mostly some of the Navy Greens and Greys in use at the time. It was not uncommon to see a mix of warhead colors on a given boat. The bodies were pretty much natural metal with a varnish like coating that had yellowish tones with black streaks. Later I think some of the bodies may have been painted black. Some torpedoes were painted in the same camo colors and patterns as the boat.
Boat leaving the Elco factory in Measure 31/5P camo. Note painted torpedoes.
Here is a link to the pT171.org site with a photo of a camo painted torpedo.
http://www.pt171.org/PT171/action/target39.html
I've been told by vets that I got it pretty close. The photo flash washed out the slight yellow tint on the body.
Here is a photo of a torpedo used on a restored Higgins boat on the West Coast.
In this photo from '43, you can see the natural bronze finish of the torpedoes in their tubes.
I hope this helps.
Ed