Dan23

Answer: It most likely represents varying power levels. Think of fire; as its temperature rises, its color changes. Energy weapons are likely similar.

Answer: There's no explanation. It could be that there are a variety of uniforms that personnel can wear, or regulations have changed. Most likely, it was a production choice to make subtle changes to the costumes.

raywest ★

Answer: If you're referring to Dress, Combat, etc, then the answer is obvious. If you're referring to green vs gold, then the answer is, "He didn't" - it was always green. The lighting and colour processing method of film back then made the green appear yellow on screen. Although there WERE a couple of green uniforms that were made of different material, one being more reflective than the other, so one always consistently looked yellow on screen, and the other occasionally looked its true green colour. But not often, the lighting AND post-processing had to be perfect to show the green.