Let me start by acknowledging that I am not a human factors expert. However, when we consider that approximately 8% of men and 0.5% of women are colorblind, it is our duty to search out experts and then make informed decisions about the Human Machine Interface (HMI) for our industrial automation and control systems.
Recently I posted an engineering brief featuring the Schneider Electric ZBRM222B0 handy box as pictured in Figure 1. This is a twin pushbutton device for remote (Zigbee) control of your machinery. Note that the product is sold with 6 colored inserts including Red, Yellow, Green, Blue, plus White, and Black. Naturally, and without thinking, I clipped in the red and green pushbutton cap inserts (lower left). Looking back, I wonder if this is the best choice.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Certify It → Human Factors
Difficulty: 
System Integrator — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 10 Mar 2026
Figure 1: Test setup for the Schneider Electric Harmony ZBRRA receiver and the ZBRM22B0 dual remote wireless pushbutton.
What is colorblindness?
Color blindness is not one thing as it can vary by individual. With regards to our selection of pushbutton inserts, there are three general types of color blindness including:
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red-green which is the most prevalent
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blue-yellow is rare
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total is also rare
What options are available to accommodate color blind personnel in an industrial factory floor setting?
Based on this very simple analysis, we can do better than selecting red and green. A high contrast black and white or black and yellow may be better. Then again, we need to find a balance as the non-color-blind operators are implicitly trained to look for the familiar green and red controls and indicators.
The good news is that we have options. Understand that industrial controls are almost always sold as members of larger families. This is especially true for selector switches. Consequently, there will be many accessories and options to configure the devices to your specific needs.
Up to this point we have been concerned with the color of the switch cap. We could keep the red green color and add caps with markings such as the red with “O” and white with the text "SILENCE".
While not necessarily applicable to the Schneider handy box, there are other alternatives such as adding text to the switch bezel, labels or shaded areas in close proximity to the switch, and switch caps with a variety of tactile surfaces. For more information you may be interested in the Schneider brief for building operator workstations. Also, given the complexities of the HMI you may want to consult with a human factors expert (ergonomist). They have a keen eye and can see things that often go unnoticed.
Tech Tip: Be sure to review the Schneider product guide to determine related accessories such as the pushbutton caps. Also, we should aspire to follow the standard ISO symbol conventions for controls such as Off and On.
Parting Thoughts
Would you agree that designing industrial equipment is an art?
There are so many things to consider. It’s never enough to just get the machine to function. We need to consider all the ways in which the operator and technician may interact with the machine in both normal and abnormal situations. As indicated in this note, we must design the HMI with clear easy to understand controls to accommodate the workforce needs.
Best Wishes,
APDahlen
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About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.