Re: Divisions, Insignia, Uniforms and Assignment Patches
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.
You already provided the answer: Back in the 1960's during TOS' original run there were still many households belonging to a "species with monochromatic" black & white only television sets.
"The first duty of every Starfleet officer is to the truth" Jean-Luc Picard
"We can't solve problems by using the same kind of thinking we used when we created them." Albert Einstein