I have been going through a rewatch of all trek in a chronological order with my wife, and as we are into season two of TNG she posed a question that I couldn't answer.
That Question is: If Data holds both the title of second officer and science officer on the Enterprise, Why is his uniform gold, which would indicate engineering or security? Is there a in-universe or production reason for his gold uniform?
Outside universe explanation, Data looked better in a gold uniform.
In-universe explanation, The Operations position was something new created for TNG and that was in the gold department along with engineering and security. Data was more of a gold shirt officer with command experience. Spock himself was a first officer but wore a blue shirt since he was also the science officer.