Colour Blindness, Network Diagrams and Reliability

It’s a lesser known fact that one in ten caucasian males have colour blindness. In networking, we often rely on colour diagrams and coloured cables for key services in critical environments. And yet, many people prepare diagrams and cabling plans using colours that will make it difficult to use for colour blind people, and these can lead to errors for our so-called critical infrastructure.

The two most common forms of colour blindness are:

  • Red-green deficiency (deuteranopia). This is the most commonly diagnosed deficiency. People with this condition cannot distinguish certain shades of red and green.
  • Blue-yellow deficiency (tritanopia). This is a rare condition where it is difficult to distinguish between blue and green. Yellow can appear as a pale grey or purple.

Testing for Red-green deficiency (deuteranopia) is quite simple through the use of colour blot cards. If you can’t see the numbers in the image below (for example) then you have the problem. red-green-color-blind.jpg

Although you should always consult a professional, there are any number of websites that have sample screening tests for a quick check to see if you have the problem.

Where this matters

I have deuteranopia, and occasionally, there are items on network diagrams that I simply cannot see, and for certain types of high density cabling (think 100 core cable bundles) I cannot differentiate between the colours of some cables. Someone has chosen colours that make it difficult to see the data on the page, cable sheath or whatever.

Where this matters is in mission critical designs for high availability networks. It’s possible to put information or data that could be missed by a perfectly competent individual when scanning a document (either on paper or on a computer screen, it makes no difference). It’s also possible that a colour blind person may not use the correct cables for a given task, thus causing sequential failures. And so on.

Understanding Solutions

Take an example of traffic lights, although most people can see at least some red/green there are some people who cannot see the colours at all. The design of traffic lights is such that they are ALWAYS vertical, and the contrast of light is detected. So even if you can’t see the “RED” light, you will see the contrast of bright / dark in the right location.

That’s the worst case for complete colour blindness, but that’s rare condition. And traffic lights are designed to handle it.

Rules of Thumb

So here are some rough and ready rules of thumb for you to start thinking about:

  • if you are building mission or life critical designs, then get everyone tested. A one in ten impact rate is very high. At least, use the Internet sites for a preliminary screening.
  • when preparing design diagrams, choose high contrast design colours so that data will not be lost.
  • avoid using red and green colours where you can.
  • choose blue, yellow, green colours instead.
  • avoid using red and green directly next to each other.
  • there is no cure for colour blindness
  • people will varying degrees of colour blindness. I see red and green more or less OK, but I have a lot of problems seeing red/green shapes together. Don’t assume you know what other persons condition is.
  • If you are colour blind, then tell people. Most people don’t know.

The EtherealMind view

  • Human Infrastructure is the most important asset in functioning computer system. Hardware and software come second to the people. ( This is often forgotten ).
  • If you are really building critical infrastructure ( which very very few busienss actually are, mostly they are just pretending), then environmental issues like personal safety, tiredness and motivation affect performance and the business outcomes.
  • colour blindness and other medical situations are just part of planning for an infrastructure.
  • find out if you are colour blind, understand what mistakes you might make, and work to eliminate them.
  • people matter. Even managers and marketing people matter. But engineer people have different requirements though and we need to be engineering ourselves to get the best performance.


Colour Vision Defiiciency – UK National Health Service

Other Posts in A Series On The Same Topic

  1. Free Custom Handwriting Font for Network Designs (14th August 2014)
  2. Network Diagrams: Font Selection and Production Context. Choosing Slab or Thin fonts (9th June 2014)
  3. Book Release: Tips on Using Visio To Make Network Diagrams (27th March 2014)
  4. Network Diagrams: Drawing Overlay Network Layers (14th March 2014)
  5. Network Diagrams: Choosing Better and Free Fonts (10th January 2014)
  6. My New Diagram Colour Scheme "Old Disco Style" (24th September 2013)
  7. On Diagrams and Information (10th September 2013)
  8. Colour Blindness, Network Diagrams and Reliability (3rd March 2011)
  9. Designer or Engineer, Artist or Painter (19th January 2010)
  10. Network Diagrams: Rotating Text on a Line (1st October 2009)
  11. Network Diagrams: Tips for Printing from Visio (22nd September 2009)
  12. Network Diagrams:Zones on a diagram with Visio shape union (31st July 2009)
  13. Network Diagrams: Drawing complex VLAN Networks with IP Addressing (7th July 2009)
  14. Network Diagrams: Drawing Freehand Curves (and then fixing them) (23rd March 2009)
  15. Network Diagrams:Aligning Shapes (12th March 2009)
  16. Network Diagrams:Locking the Background Shape (10th March 2009)
  17. Network Diagrams: Labelling an VLAN/IP Segment (9th March 2009)
  18. Network Diagrams: VLANs and IP Subnets (8th March 2009)
  19. Network Diagrams: Drawing the Background Shape (6th March 2009)
  20. On the Art of Network Diagrams and Presentation (4th March 2009)
  • Erik P

    Nice post, I have the same issue myself. This can also be an issue in color-coded project Gantt charts. I actually had an enterprise customer CIO request the project manager to modify the Microsoft Project file because he, too, is color blind.

  • Aaron

    Working with several color blind engineers over the years has taught me to use different line patterns (like solid, dotted, dashed, etc.) on network diagrams. While I can follow a red line across a 36″ diagram, there are other who cannot. In my previous life, we also chose our cabling colors based on the input of one systems engineer who happened to be color bind; if he could tell the differences among the cable colors, then we all could.

  • Phil

    Nice post. It always amazes me how many management vendors insist on using traffic light colours for alerts without any other differentiation, making it useless for ~10% of users.

  • Atle

    Nice post Greg. This is stuff most people don’t think about. But they should. I have deuteranopia as well, and can relate well to the issues you describe. When it comes to text, I have problems catching text marked red, so in all of my e-mails, for highlighting, I use red bold text with a yellow background on the text itself, so it stands out more. Makes it easier for me, and hopefully everyone else who is reading the text in question.

  • misha

    Nice post.
    I am colorblind working in networking field and biggest problem for me is to distinguish colors of the led lights on network equipment. The only thing that I can do, is to carry the laptop and connect directly to devices and monitor interface states via CLI.
    Rules and advices given here are very useful. (Will share with my coworkers)
    Fortunately, network diagrams and documentation provided by other engineers, were easily readable (so far).

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  • Raymond Eubanks

    “traffic lights is such that they are ALWAYS vertical” There are traffic lights in Texas that go horizontal..