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 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.