I'm currently in a re-watch of TOS, and while I am thoroughly familiar with the show after many, many
years of watching it, I've found myself asking a new question about the uniforms.
The colors of the uniforms seem to denote divisions - gold/green for command division, red for services support, and blue for sciences. Then the officers have an assignment insignia on their chest, within which is another symbol. Those symbols are a star, a spiral, and an oval embedded in a circle (more or less). The star is, as far as I can tell, always
on gold/green shirts, the spiral is always
on the red shirts, and the oval is always
on the blue shirts. This pairing of color and symbol strikes me as redundant. Why a color and a symbol that convey the same information?
My first thought was that the pairing is deliberately redundant, to aid any individuals with color blindness, or possibly individuals from species with monochromatic vision.
My other thought was that the symbols could
be mixed-and-matched, with the spiral/oval/star suggesting a subdivision within the larger division denoted by the shirt color. Thus Scotty, for instance, would wear red as an engineer, but as a chief engineer, he could've had a star in his assignment patch to indicate his command authority in engineering. Or the astrobiologist Ann Mulhall could've had an oval in her assignment patch despite wearing services red, to indicate her scientific specialty in the services division. We never saw any other pairings like that, did we? I'll be watching for any throughout my latest tour through TOS.