Colors and equipment states on HMI screens
Why modern HMIs are mostly grey: color reserved for abnormal conditions, consistent state indication, analog values with context, and avoiding color-only information.
The principle
The traditional "colorful P&ID" screen — red/green pumps, blue tanks, 3-D pipes — makes abnormal situations hard to see because everything is colored. High-performance HMI practice (as reflected in ISA-101) uses:
- neutral grey backgrounds and equipment;
- color only to attract attention to abnormal conditions and alarms;
- alarm colors used for nothing else.
A consistent state scheme (example)
| State | Indication |
|---|---|
| Stopped / closed (normal) | Dark grey outline or fill |
| Running / open (normal) | Light fill or white outline — still neutral |
| Transition (opening, starting) | Blinking outline or arrow |
| Fault / alarm | Alarm color by priority + symbol |
| Manual / local mode | Small letter indicator "M" / "L" |
| Interlocked | Lock symbol |
| Out of service / simulation | Dedicated pattern, clearly visible |
Whatever scheme you choose, document it and use it everywhere. Note that the red/green meaning of running/stopped differs between industries (power plants often use red = energized), which is another reason to keep normal states neutral.
Analog values with context
A number alone does not tell whether it is good. Show values with units and a small bar or moving-analog indicator with normal range and alarm limits, plus short trends for key values. The operator sees deviations before the alarm.
Accessibility
About 8 % of men have some color-vision deficiency. Never encode information only by color: add shape, text, position or a symbol (e.g. priority number in the alarm icon).
Connections
Open in Knowledge Graph →Loading the map…
Sources
Updated 2026-10-02