Here is a key to the color codes on a Juniper SRX. You can determine what LEDs are turned on by either looking at the front panel of the SRX or doing a show chassis craft-interface command.

LEDs on front panel of an SRX

Alarm LED
Color Description
Red steady critical alarm
Amber steady major alarm
Green no alarms
Off device powered off



Status LED
Color Description
Green steady normal
Amber steady startup
Red steady device failed
Off device powered off



Power LED
Color Description
Green steady normal
Amber steady device is gracefully shutting down
Red steady power supply problem
Off device powered off



LEDs on the front panel of a Netscreen


CPU Utilization
Color Description
Green steady Current level of CPU use
Off Less than 5% CPU use



PWR LED
Color Description
Green steady System is receiving power
Off Power is not on
Red solid power supply problem



Status LED
Color Description
Green Blinking System is receiving power
device is gracefully shutting down
Red steady power supply problem
Off device powered off



HA
Color Description
Green steady Indicates this module is the master
Amber solid Indicates this module is a slave
Off Indicates no HA activity seen



Alarm
Color Description
Red solid indicates a critical alarm which could mean the system crash or failure
Red blinking Indicates that an alarm has been triggered
Amber solid indicates a major alarm which could be low memory
Off No alarms detected



Flash
Color Description
Green Solid Flash card is installed
Green blinking Indicates flash card activity
Red Blinking Flash is completely used or error has occurred with it
Off No flash card detected in slot