From the SunFDDI SBus Adapter 5.0 User's Guide:

red -   Either the driver is loaded and the interface is NOT
        configured or the drive has not been loaded.

amber - Interface configured.  No valid line state to an active FDDI
        network exists.

green - Connection established to an active FDDI network.

blinking green - In a dual-ring environment: Invalid connection
        In a dual-homing environment: Normal. The connection is in
        standby mode.