The D'ni people used a visual color symbology. It was based on a 6-basic color system, represented as circular eyes. Obviously there were intermediate shapes between these "keys", indicating hue combinations. Gehn employed these symbols with his Fire-marble Domes. The circumference of each dome had a series of 36 symbols.
The colors were:
- Horizontal closed eye (a circle with a horizontal bar): Orange
- Horizontal eye: Yellow
- Fully opened eye (a circle with a dot): Green
- Vertical eye: Blue
- Vertical closed eye (a circle with a vertical bar): Purple
- "Cat" eye: Red
Gehn, being obsessed with the number five, considered that the 6-color basis was superficial, and was attempting to determine if the symbology reflected the principle on five. While assigning a color code to the Dome of each island, he left out Yellow, and assigned the rest to the five islands of Riven: Book Assembly Island (Purple), Prison Island (Blue), Temple Island (Green), Survey Island (Orange), Jungle Island (Red).