The first one I'll share is my Dagoroth settlement on Ruswono 2. Straddling the divide between badlands and frigid wastes, this is one of the most prosperous settlements I've ever built, despite its inhospitable location. The cold, dry weather is offset by an extreme abundance of mineral wealth, and a source of fresh water makes irrigation feasible for farming during the region's short growing season.
Here's a view of the whole colony from above:

And I'll just give a brief tour of some of the colony's most important features.
In the NE corner of the colony, you can see all the pipes that serve as irrigation for an agricultural area. The first apartment block for the colony, a 4 story structure, can be seen just east of that area, and the interior of its top floor is visible. The colony's extensive machinery grid, with its all-important chemical power generator, can also be seen, as well as the marksmanship targets and military training area.

The colony's NW corner can be seen here. A graveyard with a minor monument is surrounded by a moat, as is the colony's primary monument, The Iron Tower. The top-down view only shows the highest floor, but the tower near the river is 20 stories high and filled with opulent furnishing. The hospital can be seen in the SW corner of the screenshot, but it's currently over-filled with patients suffering from corpse rot.

The colony's SW corner is somewhat sparse, containing the settlement's landing zone for ships, a two story prison, and and a pasture area for holding and training captured creatures:

The colony's SE corner, however, contains its great hall. This is a 6 story structure with a well furnished socialization area at its base, a secondary hospital area, luxury apartments, and elegant office space, for the colony's bureaucracy, on its top floor. Some old, single-family dwellings from the colony's early days are also located here.

The socialization area:

The child care area:

The secondary hospital:

The colony thrived and grew to a population of nearly 200, within less than two planetary years:

Unfortunately, its great material wealth attracted the attention of a covetous foe, causing a great battle occurred during the colony's second summer. Barbarian raiders sought to plunder the colony's extensive material reserves and supplies of consumer goods. Despite heroic resistance, its defenders succumbed in the face of overwhelmingly superior enemy forces. All the colony's citizens were massacred, and civilization came to an end on Ruswono 2.

I'll aim to post some of my other favorite colonies when I get the chance, but I'll always miss this one.