I'd like to see different architecture for each civ, so basicly the same buildings look different depending on the race that inhabits the world. I don't imagine this would be too difficult to implement, as it's only the appearance of the buildings we're talking about here, not really their function or anything and it would do a lot to give each race more character. Each colony building has a particular appearance which should be distinctive enough to be immediatly recognised and would give each race some more character. Each of the major races should have a distinctive colony appearance at least, and the minor races too if it can be managed, though this isn't essential. Buildings should always mantain the architecture of those that built them, so older alien buildings can potentially be seen on the same planet alongside newer human buildings. Galactic movements (including the I Leugue) should build buildings of the architecture of the first race to colonise the planet so such planets keep their distinctive racial architectural style. The kind of buildings I'd imagine each alien race would have I submit below.
Altarians- Smooth domed buildings, predominately light blue in color, with plenty of arcane symbols down the walls.
Torians- A combination of smooth curves and sharp spires and edges, predominately emerald green.
Arceans- Heavy and bulky looking building, predominately stone-brown and with few aesthetic touches.
Drath- Buildings usually archaic and fortress like with flat rooves, battlements and sometimes towers.
Korx- Largely charmless architecture, with plenty of poorly thought and clashing aesthetic effects.
Drengin- Rusty looking hexagonal structures, reflecting the Drengins real lack of interest in either appearance or design of civilian structures, militery structures should be pristine, manacing looking and painted in black, red and orange colours.
Yor- Industrial looking steel structures, with plenty of purple lights and touches. Should look in-organic and artificial.
Thalan- Huge earthen mounds of varying size (similer to termite mounds). Tiny lights should be visable on the flanks of the mounds to give them a lived in appearance.
Iconions- Pyramidical and studded with arcane symbols down the sides. The buildings should look alien, exotic and arcane.