On the front panel, there is an LED light called ID and DIAG.
The ID LED light can become OFF or turned into solid BLUE.
The DIAG LED light can become OFF or turned into solid GREEN.
The ID LED is theoretically used to find a device in the lab. The idea is that you would turn it on/off from the CLI and then go in to the lab and look for the device with the light ON. However, the current ISG does not support the command.
As for the DIAG LED, when the customer diagnostics boots up, the DIAG LED is set to Green. When exiting the customer diagnostics image, the DIAG LED is turned off. The default state for this LED during bootup is OFF.