A common question is what do the stack light colors mean. There is some flexibility and this can vary from facility to facility. But in general the colors have a standard use.
The Five Standard Colors
Red signals an immediate problem. It can be a fault, a stoppage, or a safety issue. Production is not moving, and someone needs to act. Keep red reserved for critical conditions only.
Amber is your early warning. The process is still running, but a condition is developing that needs to be addressed.
Green tells you everything is working as expected. The station is running, the process is on track, and no action is required.
Blue means the operator needs support, not an emergency, but something that requires another person. It could be a material replenishment, a supervisor's question, or a changeover.
White has no fixed industry meaning, which makes it useful for signals that are specific to your process. Facilities use it to indicate shift changes, production goals hit, scheduled maintenance windows, or any custom status that the other four colors don't cover.