I've worked that out for myself. I'm not going to call it head cannon because so many versions of pre-refit Enterprise have now been seen (a couple of TOS changes, TAS, DISCO, TOS-R) and it might not work for anyone else but... consider America's first true spaceship. No not a mercury capsule. Depending on the flight, the X-15 could be coated in ablative material and presented a smooth white featureless design, interestingly with red markings on the side . So for me, for whatever reason, for a few years most Connies ran covered. Shielding, stealth, just personal fleet preferences. No idea. It covered all the detail below. Starfleet went through a period where It was not keen on glowing nacelles, as well, which lasted even longer. on the subject of the aesthetic, of all the show eras TOS is the one the stands out and is my favorite. It is the most alien. They weren't trying to make this future completely relatable. Why do people hang swatches of the same material as their blanket on their walls in lieu of photos or their walls? We don't know. We don't always have a frame of reference for this culture. They eat things that some times seem familiar, sometimes definitely not. The colors are garish and bright but it works because again, that's how it is. I'll take a moment to stand up for the blinkenlight interfaces as well (not the tiny viewscopes though). I used to just imagine that they had writing one couldn't see, etc, but I recently got a combination synthesizer/drum machine that does use a jolly rancher type display, and it's only intimidating for about 5 minutes. It's far less thought consuming once you understand what you are operating then having to check back and forth on a monitor and touch typing. So I would say this is one where TOS was actually WAY out ahead of the pack. I think non-written color and velocity touch interfaces will actually become more common over time. and they'll be added to the things Trek got right, along with cell phones, stun guns, etc.