HMI standard regarding symbol color


Thread Starter


A few months ago I posted the following message:

"During the design-phase of SCADA-applications there sometimes is confusion about the status of the symbols (e.g. valves, pumps etc.) and their color.
There is no HMI standard regarding symbol color that I am aware of. There does seem to be industry specific guidelines, however. Some industries like red to be the energized/on state, others use green for the same condition and so on.

Is there a HMI standard regarding symbol color or is there a report where the topic of symbol color is addressed?"

Your reactions were very interesting and helpful. The subject 'Symbol Colors' started a good debate on
I'm at this moment busy developing a standard for our company and want to ask you to react again.

My statement is: "Go for a clean screen. Grey for inactive, green for active and red for alarm."

What do you think? Any idea, own experience, example or help is welcome.


Tom Tuddenham

Hi Xander

I don't know if any "standard" colour scheme is appropriate within the SCADA domain. Colours should reflect the business of the people we're finding solutions for, rather than engineers telling our customers what's best for them. Any colour is loaded with potential meaning that can vary from business to business. For example, in one enterprise red may mean "stopped", whereas in another green may be "clear to start". These states are virtually synonymous from an engineer's point of view (i.e. "the machine is stopped") but have a different operational sense in the different contexts.

I'd be very wary of dictating any common colour scheme across the industy. Of course there are going to be similarities between applications but nothing guarantees that what is black for one isn't white for another (or grey for that matter).. :)

We have TWO different standards on the pipelines I work on. It's rather confusing to ME, as the control systems guy, but the operators only work on one pipeline or the other, and couldn't care less.

One pipeline uses (my preference) red for stopped or closed, yellow for in transit or starting/stopping, green for running or open, and flashing red/black for an error state (ie stuck valve or bad status coming in to PLC).

The other pipeline uses pale blue for stopped, magenta for in transit, yellow for running, and red for error. Looks like a dog's breakfast to me, but it's worked for them for many years.

My belief on the subject of color is that standardization IS required within a given SYSTEM only. Beyond that it's just too much to ask to try and find a common scheme for everyone. There are many years of history behind every scheme. As long as it works and is consistent for the people who use it then it's fine.

I wrote a similar MMI (now HMI) design standards document for my project 6 years ago. I found several standards to reference such as ANSI/ISA S5.1 and DOE-STD-1062 "Human Factors Engineering Design Criteria", but the best reference was an common sense article in InTech magazine:

Toffer, D.E., "Designing an Operator Interface? Consider User's 'Psychology'," InTech, ISA, Nov., 1995, 52-56.

It has a nice screen hierachy approach and discusses using colors that make sense to your customer.

Good Luck!

Chip Hinde
Los Alamos National Laboratory
I agree a certain color sceme is in not suitable for every system. A lot of companies have their own standards, for example based on colors they used when the process was controlled manually (operators and maintenance techs are used to it).

In some situations however, a company doesn't have a color-standard of its own. In that case we want to be able to present our own 'house-standard' (that of course is open for discussion).

Thank you all for your reactions!
Sounds good. You may want to consider the CE standards for stack light colors. White for ON but inactive (Grey is good), red for alarm state (you can even make it flash if you want to), yellow for warning (not detrimental but could cause a problem), green for normal operation - on. Blue for needs operator input - something like a reset button after a fault. Good luck.

Ronald Powers
SR Product Specialist-HMI
Validation Center
Siemens Energy & Automation
5300 Triangle Pkwy
I didn't notice if the issue of color-blindness came up yet, but since more than 8% of the population suffers from this condition, it's likely that a color blind operator will eventually use your HMI. I've seen many OI's that use Green to indicate normal and red to indicate alarm. Red/Green color blindness is the most common form - so there's a strong possibility that a color blind operator would not notice the alarm condition without some additional indication.

General software development user interface guidelines suggest never using color as the primary indicator of a condition. This is likely the easiest solution since simply adding the word "Alarm" or "Normal" to a graphic would eliminate the problem.

Either DuPont or Dow released a HMI color and design standard 6 or 7 years ago. I had a copy of it then but can not locate it now. Maybe someone still has it or knows where that guide could be acquired? It was the most comprehensive and useful standard I've ever seen.

Jeff Dean
[email protected]

America is not like a blanket--one piece of unbroken cloth, the same color, the same texture, the same size. America is more like a quilt--many patches, many pieces, many colors, many sizes, all woven and held together by a common thread." - Henry M. Jackson
You may be interested to know there is a euronorm specification, EN60204-1 which covers lamp colors etc., but I suspect it is pretty widely ignored. Red is for emergency or hazardous conditions, yellow for abnormal, green for safe, and blue for condition which requires operator. Not much help if you want to know what color to make a motor running lamp. We have built panels for a major oil company who used green for the normal condition, yellow for abnormal, so the annunciators or screens show all green when the plant is running OK.

Scott Maynard

A persons eyesight will deteriate dramatically over their working life, and a old experienced operators capacity to differenciate between some colours in a HMI will be similar to that of a colour blind co-worker.

We always have a alphanumeric identifier next to any shape that represents a control or equipment state.

A motor will therefor not only change colour, but the identifier will also change to allow operators to determine state.

'I' would indicate 'In service or running'
'A' would be 'available'
'O' would be 'Out of servive or no power'

Any colour code that would be deployed internationally would not work as different cultures have such different ideas.

Maybe a better way is to create a system that would inherit the colours from a source external to the display environment - maybe as a display is invoked.

The internal code and conditioning would be the same but each site would then have a tool that could easily alter colours to their own preferences. After a while they would be standardised but changes could be made almost instantly and it would give operators an increased sense of control and ownership during commisioning.

just some thoughts....!
There are a number of commonly seen conventions:

1) red on (or open)-green off
2) green on-red off
3) green on-white off
4) yellow/amber on, green off

I have also seen graphics done with green or red on, and invisible for off.

One customer insisted that it was green for energized and red for de-energized, so that N.O. valves were red open and green closed, while N.C.
valves were red closed and green open.

Another customer had color coded all the pipelines in the graphic and the graphic symbols were invisible to indicate off or closed, and the pipeline color to indicate open or on.

The key is to be consistent, both within the graphics system you are providing, and any existing systems.

People can argue what is the best from a human factors perspective, but its mainly a moot point as most plants have some kind of standard, or at least a convention, and it is best to follow it to avoid confusion.

I sort of like either invisible or white for off/closed, and green for on/open. This makes it possible for the colorblind to see easily the status of the item in question, and I can use flashing red for an alarm.

But quite frankly, most (maybe 75%) of the systems I do, end up using red and green (about half of these use red=on and half use red=off), and alarm indication is a small alarm tag near the item in question.

Bob Peterson

I've always done the "green open" "red closed" for valves, but all of my HMIs have been for operators. I have heard that maintenance people are the ones who use the "green closed" "red open" approach, as does the power industry for CB settings. In both those cases the idea is that green indicates that downstream of the device nothing is happening- so it's OK to break open a pipe or grab a conductor. Anyone ever actually done it that way?

Paul T

Rob Antonishen Ontario Power Generation

> HMIs have been for operators. I have heard that maintenance
> people are the
> ones who use the "green closed" "red open" approach, as does the power
> industry for CB settings. In both those cases the idea is that green
> indicates that downstream of the device nothing is happening-
> so it's OK to
> break open a pipe or grab a conductor. Anyone ever actually
> done it that
> way?

Except CB's are the opposite of valves :)

Open valve = flow, Closed valve = no flow
Open CB = no flow, Closed CB = flow

In my company we use a green symbol to indicate a closed CB - or system "normal" and a red symbol for a tripped CB, or "abnormal"

On a lighter note, I knew an elderly lady who was always confused by this. She would say "Open the light [switch]" when she wanted a light on. I guess she was thinking it was like a blind or shutter over a window...

-Rob A.


Heavner, Lou [FRS/AUS]

I've also seen "I" used to indicate a device was interlocked and "F" used to indicate the a device had failed. There are probably others. Defining a standard for this might be as useful as one for colors.
Of course, there is a convention in the pump station control business that would interfere with your I-A-O nomenclature, Lou: H-O-A for

Walt Boyes

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