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Design Notes on Colour Blindness, Part 1


I’m definitely stating the obvious when I say that we all see colours differently. Who’s never gotten into a discussion about a certain hue being more red or more purple? More blue or more green? Mostly this is due to environmental and psychological factors, but for some people the retina will not pick up certain light frequencies. In this case we are talking about so called “colour blindness”.

But how does this all relate to design and more specifically to the design of Eurorack module panels? Well, it has quite an impact, but let me start from the beginning.

If you have been following this blog for some time, you’ll probably know that my actual job is not writing articles, it’s designing stuff. Among other things this stuff happens to be Eurorack module UIs and panels. Together with my wife Elizabeth, I run a small design studio called Papernoise. We are probably best known for our work for Mutable Instruments, but we have also designed panels for Hexinverter, Alright Devices, Rabid Elephant and others.

For this article I’ll mostly focus on our work for Mutable Instruments, which was carried out in close collaboration with company owner and module designer Émilie Gillet.

We had established a series of design rules with Émilie early on. Modules were relying on simple monochromatic LEDs to give the user feedback about the module’s activity, while the colours purple and turquoise (originally defined for the company’s visual identity) were used to make it easier to associate certain controls with their relative CV inputs.

So, for example, on Grids the 3 LEDs light up to signal that a trigger pulse is being output on the relative jack. The FILL knobs are turquoise and their CV inputs have the label surrounded by a rounded rectangle of the same colour.

As the functionality on the modules became more complex, there also came the need to find a component that could give a wider range of feedback without taking up too much space. Red/Green LEDs were introduced.

I think the first module to use such an LED (limited to the red and green hues) was Tides (MK1), where it was employed to display the chosen mode and the frequency range. As you can see in the image below, near the big button, top left, the turquoise icon represents an AD envelope, black is cycle (LFO/VCO) mode, while the purple one is for the ASR envelope. By pushing the button the LED would cycle between green (AD) to off (LFO/VCO) to red (ASR).

I asked Émilie why these LEDs are so popular, this is what she said: “These components are actually extremely popular for two reasons. First, historically, the first LEDs that were manufactured were red, and then green. Blue LEDs (which later allowed RGB LEDs) are more recent inventions. Secondly, the prevalence of the green = go, red = stop colour code, inspired by traffic lights, makes the bicolour red/green components extremely common. They are widely available simply because there are thousands and thousands of industrial devices designed in the 80s and 90s which still require them!”

Another thing about red/green LEDs is that by mixing these two colours you get yellow, which is something that got used extensively on newer Mutable Instruments modules.

These LEDs are also used on many electronic instruments and devices. For example, Elektron used these on many of their products, before moving to illuminated pads/buttons. The Octatrack MK1 I have relies heavily on red/Green LEDs to communicate states and activity.

Many popular modules by Mutable Instruments, like Clouds and Rings, use Red/Green LEDs for user feedback. With Rings we further developed the pattern introduced with Tides, adding the colour yellow to both the panel labelling and the LEDs. This would then be used as a standard for many subsequent modules. Just like on Tides, Rings’ modes are represented by icons and printed on the panel using the colours turquoise, yellow and purple. By pushing the mode button the LED changes its colour to tell the musician which mode is active.

This worked well and enabled us to keep the size of the modules compact and display-free, while still offering a pretty wide range of features. Also, it was perfectly consistent with Mutable Instruments’ existing visual identity.

Then, 2 years ago, Émilie and I had a bit of an “aha” moment. We realised that a lot of people were impacted by colour blindness and modules like Rings could be quite challenging for them to use. We had somehow always been aware of the existence of colour blindness, but we weren’t aware of the scale of it, something I’ll get back to later in this article.

I started to talk to modularists to see how they coped with the LEDs and the prints on the panels and started a thread on the topic, on Modwiggler, probably the most popular online forum about modulars, and on the Mutable Instruments Forums.

Lots of people sent me their feedbacks and told me about their experiences.

Most people found ways to deal with the problem. Some might ask their partners “hey what colour is the LED right now?”, some just used their ears more, others memorized some reference point and then counted from there. In spite of this, many were understandably frustrated, so we decided to do something about it.

But before we get into that, you might be wondering…

Colour Blindness, what is it really?

Of course the word “colour blindness” is a bit misleading. When you’re colour blind it’s not like you see everything in b&w, or rather, that is one of the many existing types of colour blindness called monochromacy, which is very uncommon. In most cases you do see colours, but your perception of them is different. Some of the frequencies are absent.

Even after digging into the matter for some time, I’m definitely not an expert. There’s a bunch of useful resources online where you can read more about it, but roughly, this is what we’re talking about:

about 1% of the male population has deuteranopia, i.e. the retina does not register the medium wavelengths related to green. People with deuteranopia basically see everything in blue and yellow and shades of these colours. They basically don’t see or have trouble identifying red, green, orange, purple and cyan.

5% of the male population has deuteranomaly, which is a variable inability to perceive the above wavelengths. People with this type of colour blindness might or might not be able to see either green or red.

1% of the male population has protanopia and 1% Protanomaly. This type of colour blindness affects long wavelength cones (red) but the effect of this is almost the same as the above.

All of the above types of colour blindness are extremely rare among women.

Tritanopia and Tritanomaly affect the short-wavelength cones. People affected by it do not see yellow, green and blue, everything to them is red/cyan. This type of colour blindness is very rare but affects males and females equally.

Roughly we could say that about 8% of the male population and a very small percentage of the female population does have a hard time discerning between colours like red, green and purple, which is actually a lot of people if you think about it. So it’s definitely worth considering how to not make the instruments we design usable for them.

This is it for today. In the next part I’ll get into the details of what we actually ended up doing about this.


Graphic designer, illustrator and soundmangler. He makes music as kurodama and as part of the electronic music duo kvsu. Together with his wife Elizabeth he runs Papernoise, a small design studio located in northern Italy, specialised in graphic design for the world of music.

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