ISO Standard Human Spaceship: They’re “realistic” designs, involving designing for microgravity, with nuclear engines out on the end of long trusses and no particular need to worry about aerodynamics or putting all your machinery inside the pressure hull, but —
1. They’re not painted grey or left as uncolored metal. This is not the ocean, there is no stealth in space, and there’s no real advantage to being a bland and neutral color. And while you could save some mass by leaving off the chameleon nanopaint, true, there is another consideration – namely, in close orbit operations, or while alongside a habitat, people can see you, and people who can afford private spaceyachts want them to look gorgeous, of course, but more importantly, everyone from Stellar Express to Constellation Dream-Lines spent a lot of money on their corporate color scheme and logo, and they want it splashed all over the hull in living animated Technicolor. Half the captains in space don’t even turn the running lights off when they leave orbit just in case someone might be pointing a telescope their way.
(ISS and IMS ships are generally colored Imperial indigo, with gold trim. Crimson striping is optional on those vessels operating under diplomatic privilege.)
2. Being visibly constructed from riveted plates is distinctly disfavored; rivets imply seams, seams imply weak spots, weak spots involve the possibility of messy vacuum-aided death. While it would be ludicrously inefficient to nanogrow an entire hull as one seamless unit, they do like to use nanopastes to make the seams go away afterwards. They do have the usual number of ports, sensors, and antennae attached in various places, though.
3. While you can certainly draw a box around them – and goodness knows a lot of less, ah, aesthetically sensitive species seem to think that the ideal shape for a freighter is a large steel box with an engine stuck on one end – it would be hard to describe a typical Imperial vessel as “boxy”. As soon as autofabrication made it possible to do grand, sweeping pseudo-organically curved shapes, naval architects dug their last few centuries of idle sketches of cool-looking but impractical ships out of the closet and ran with them, at least for civilian use – often in shapes that don’t enclose, but do conceal, all the heavy machinery and massive spherical fuel tanks and cryocels mounted on trusses outside the pressure hull. Or at least the bits of it that don’t look cool, while coyly revealing the parts of it that do. (And even the military ships aren’t all that boxy.)
And then, of course, there are the thermal radiators, which often resemble great curved wings of one kind or another when fully extended, even if they’re not solid (the most common radiator types are sheets of droplets extending from sprayer to collector).
4. For reasons explained elsewhere, there are no space fighters designed to be flown by meat. Such things have negative combat advantages and no survivability whatsoever.
(As a side note, while every bit as impractically fancy, in many cases, as the extensive brightwork of Royal Navy warships or East India Company merchantmen in the old tall ship days, the colorful paint jobs and excitingly sweeping shapes serve much the same memetic purpose: “we’re rich and powerful and successful enough that we can spend lots of time and effort on this stuff without impairing the basic functionality of the ship at all, so draw appropriate conclusions before startin’ something”.)
