Since it never was put into the game and I highly doubt it ever would have, let me at least show off one of the seven Uncharteds I finished: Uncharted Sigma aka Cloud Ocean.
Uncharted Sigmas was a system somewhere not too far away from Sigma-21 and was supposed to be explored during or after the Kusari-Rheinland war. Two battlegroups, one of each house, were supposed to stumble over the system and realize that someone else had tried to settle down here years ago. The entire system was layered, in the hopes of giving people a certain Bespin/Dream Dance Zone (S:ATS) vibe.
The mid-layer of the system, slightly below the plane, was a system-wide cloud with ice crystals, including some bigger ice crystal formations which contained a few secrets to explore. These secrets had infocards, hinting the background of the system and how the two battlegroups found it.
Breaking through the mid-layer, the player would find themself surrounded by clouds. Imagine flying through earth's cloudy sky during a sunset.
Below the bottom layer was a badlands cloud - something one wouldn't find without exploring the depths of the system. The cloud was slowing every ship down, dealing radiation damage, effectively limiting the time a ship can spend inside. However, exploration would have been interesting, as a unique anomaly somewhere inside the cloud seemed to be able to reverse damages that had been suffered. A temporal anomaly? A metaphasic cloud? Hull-restoring bacteria? We will never find out.
Neither the rheinlandian battlegroup nor the kusarian battlegroup left the system - none of them managed to report back to command. The Kusarians were chased into the mid-layer, their Takeda colliding with a giant ice rock. Escape pods were launched, eight of them tried to reach the three jump holes, only to find out none of them were leading back anywhere. The Rheinländers made the same experience, their Donau not surviving the entry of the jump hole. The wreck parts are marking the horrible accident.
The defining trait of the Sigmas is less about the colors (as Sigma-21 shows) but the amount of nebulae. What the Taus have as asteroids, the Sigmas offer as nebulae. As mentioned above, the system was supposed to be in the Sigma-21 area, where white clouds are more common while the distance indicates more proximity to the Crow than to the Edge. I tried to signal that by procedurally have the more distant clouds more blue-ish while every cloud gains more red/orange saturation from the red giant in that system, giving it the Bespin-ish/Hokkaido-ish coloring. You can see the difference in some of the gifs.