Green Uniforms?

I was watching the second episode of The Original Series and noticed that Captain Kirk was wearing a green uniform. I have seen him do this before but it always seemed odd. In Star Trek, the uniform colors gives an indication of the role the officer has on the ship. In The Original Series and Enterprise red was for security, engineering and operations, blue was for science and medical while olive green was to represent command. In The Next Generation, Deep Space Nine and Voyager red was for command and gold was for security, engineering and operations.

So why do we only on occasion see a green uniform usually only worn by Captain Kirk. It turns out the material that was used to make the original uniforms showed up as gold when filmed or photographed, while the alternate uniform we sometimes see Kirk wear was made of a different material so it would show up in the color it was originally intended to be. In later seasons, there is dialog which mentions gold uniforms which put it into canon from that point forth.

Another interesting uniform tidbit. The pants they wore was dark grey but on film it shows up black.