Machine and Process Management

The Truth Behind the Colors of Pushbuttons

While preparing the launch of our new pushbuttons, our communication expert came up with the above picture, which I believe would not be out of place in a modern art gallery. It made me think a bit about the actual reasons we have so colorful products. Vibrant colors are definitely one way to give a modern look and feel to a control interface, but surely, we engineers are not only choosing the blue button because that’s the nicest color on the shelf. But actually, past the “emergency stop is a red mushroom button on a yellow background” and the most common “blue reset button” and “green start button”, I had not thought about the color choice for a long time. So, I’ve taken my best speleologist and went digging up into the color meanings for pushbuttons.

As often for industrial products, I found a couple of standards that are defining the colors and their individual meaning. The first interesting one is the IEC 60204-1 which provides guidelines for colors in both pushbuttons and pilot lights; these guidelines are presented as advices and the standard is actually mentioning that the manufacturer and the users can agree on different color choices. A simplified approach of this guideline would be :

In case the choice of color is not obvious, white & grey are the favorite recommendation.

However, through the meaning of colors is explained, the actual definition is not given in this standard. The most useful standard for color definition is, in my opinion, the ISO 3864-4, which describe acceptance areas of colors for signaling lights.

As you can see, the “Amber” color is actually quite interesting as it is covering two usual colors, the yellow and the orange.

2 pilot lights for the same Amber color

Why do we have 2 colors in that scope ? Part of the answer is technical limitations on the plastic & light pigmentations inherited from older technologies. Another reason is the geographical preferences, Asian operators being more used to the yellow for alarming compared to European and American operators who often prefer the orange.

Finally having two colors is enabling two differentiation:

  • In the very rare case where the 2 colors are used together, a control interface could indicate different levels of importance for the alarms
  • When color-blind operators may use the control interface, the distinction from the nearer pilot light can be difficult to see leading to errors. A yellow pilot light will be easier to see near a red pilot light than the orange, but an orange light will be more easily distinguished near a green light. The contrast with the other colors on the panel can then be a good guideline

Some control interfaces and simulation of how color-blind operators could perceive the same control interface.

I hope you enjoyed this small trip in the arcane of pushbutton colors. Don’t hesitate to share your opinions about color choices in the comment.

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