Regardless of any published spec, it still depends on what is reasonable and safe for the users and the process.
It depends on the situation, the process, the environment, the relevant meaning of the color in terms of the information being imparted, and the decisions made as a result of seeing those colors.
Generally, GREEN means ON.
However, it can also mean "OK to GO" or "SAFE"... in this case, is the device ON? Or is it OFF? It might very well be that the device must be OFF for the "OK to GO" or "SAFE" condition to exist.
In some situations, a string of lights might indicate the particular status of a set of valves, motors, whatever. It might be the case that all of those devices must be in a particular state before an operator can proceed with a particular action.
If the required status of the various devices is a particular combination of ON, OFF, OPEN, CLOSED, then is it better to show all GREEN if the combination is as required? Or should the lights indicate GREEN = ON/OPEN and RED = OFF/CLOSED?
An operator can make a decision much more easily if all colors are to be GREEN (for example) before proceeding. A RED would instantly show a missing condition. The operator coulds then look to see what the particular missing condition is.
If there is a multitude of various colors then it becomes very hard to quickly discern that there is a problem.
It depends.