An LED shows on or off. Equipment often has more states than that: a pump can be running, stopped, in manual, faulted or unknown, and the operator has to tell them apart at a glance. The states are declared once and the component resolves its value against them.
The severity of a state selects a colour from the active theme, so the same markup works with an ISA-101 industrial theme and with the standard themes. A state can also blink, which ISA-18.2 uses for an alarm that is waiting for acknowledgement.
This example cycles a single indicator through its declared states.
value = —