---
title: MDR Color Coding and Visual Design
description: How EN 62366-1 and MDR Annex I treat color as a safety signal, why color-only information fails audits, and the bee-mouthpiece lesson on outdoor color hazards.
authors: Tibor Zechmeister, Felix Lenhard
category: Usability Under MDR
primary_keyword: MDR color coding visual design IEC 62366
canonical_url: https://zechmeister-solutions.com/en/blog/mdr-color-coding-visual-design-iec-62366
source: zechmeister-solutions.com
license: All rights reserved. Content may be cited with attribution and a link to the canonical URL.
---

# MDR Color Coding and Visual Design

*By Tibor Zechmeister (EU MDR Expert, Notified Body Lead Auditor) and Felix Lenhard.*

> **Color is a safety signal under EN 62366-1:2015+A1:2020 and MDR Annex I, not a branding decision. Red means danger, yellow means caution, and green means safe or normal, but none of those meanings carry the full load on their own. A compliant visual design never uses color as the sole information channel and always accounts for the actual use environment, including outdoor lighting, color vision deficiency, and environmental hazards like insects attracted to specific hues.**

**By Tibor Zechmeister and Felix Lenhard.**

## TL;DR
- EN 62366-1:2015+A1:2020 treats color as part of the user interface, so every color-coded element is inside the scope of the usability engineering process.
- MDR Annex I §5 requires reducing use-related risks, and §22 adds lay-user specific requirements that make color-blindness tolerance non-negotiable for home-use devices.
- A single-channel color signal (color alone, no icon, no text, no shape) fails audits because roughly 8% of men and 0.5% of women have red-green color vision deficiency.
- Standard safety color conventions map cleanly onto device signaling: red for danger or immediate action, yellow for caution, green for safe or normal, blue for mandatory or information.
- The use specification document must describe the use environment in enough detail to surface environmental color hazards, such as outdoor light levels, reflections, and in one real case, bees attracted to a specific mouthpiece color.
- Color choices belong in the risk management file (EN ISO 14971:2019+A11:2021) as risk controls, with residual risk analysis tied to the hazard-related use scenarios that motivated them.

## Why color is a safety control, not a styling choice

Tibor has watched startups spend more time arguing about brand colors than about whether those colors communicate the right safety meaning to a real user. Under EN 62366-1:2015+A1:2020, every visual cue on the user interface is part of the usability engineering process. When a device lights up red, the user must understand, without training, that something is wrong. When it lights up green, the user must understand that the device is ready.

Felix has coached enough startup teams through their first notified body feedback round to know the pattern. The founders walk in proud of a clean industrial design. The auditor asks one question: what does the yellow LED mean, and how does the user know what to do when it turns on? The team explains that yellow indicates low battery. The auditor then asks where that meaning is documented in the use specification, how it is validated in summative testing, and what happens if the user is color blind. Suddenly the visual design is a compliance deliverable, not a styling artefact.

The MDR reference points are concrete. Annex I §5 requires reduction of use-related risks. Annex I §22 adds lay-user considerations including skills, needs, environment, age, and medical condition. Color choices are a direct expression of both requirements.

## What the standards and the MDR actually say

EN 62366-1:2015+A1:2020 does not prescribe a color palette. It requires that the manufacturer identify hazard-related use scenarios, and that the user interface design, including color, be evaluated against those scenarios. The presumption of conformity with MDR Annex I usability requirements flows from applying the standard correctly, not from picking a pretty palette.

EN 60601-1:2006+A1+A12+A2+A13:2024 adds an electrical-equipment layer. For medical electrical equipment, safety indicators must be visible, and the conventions around indicator lights and alarms intersect with the collateral standard on alarm systems. A device that shows a red light while emitting a low-priority audible alarm is sending mixed signals.

EN ISO 14971:2019+A11:2021 is the glue. Once the usability process identifies a color-related hazard, the risk control must be captured in the risk management file with a residual risk assessment. Tibor has seen auditors trace a color choice back through the risk file to the hazard-related use scenario that motivated it and accept the design on that basis, and he has seen the opposite, where a team could not explain why a particular color had been chosen.

The safety color conventions themselves are not invented per device. Across European safety signaling, red is danger or immediate action, yellow or amber is caution, green is safe state or normal operation, and blue is mandatory or informational. A device that uses red for "on" and green for "alarm" is fighting twenty years of user expectation.

## The one rule that saves founders an audit round

Never use color as the only information channel. This single rule resolves most of the common findings in one step. If the device says "charged" with a green LED, it should also display a charging icon filling up, or a text label, or a shape change. If the device warns of a fault with a red LED, it should also display an error code, an icon, or a text line. A color-blind user, a user in bright sunlight, a user viewing the device through a dirty visor, must all be able to receive the information.

Roughly 8% of men and 0.5% of women have some form of color vision deficiency. For a home-use device targeting the general population, that means one in twenty male users cannot rely on red-green differentiation. Tibor has sat through audits where a team argued that their user population skewed female and therefore color blindness was a minor concern. That argument has never held up. The device is approved for sale to the general population, and the general population includes red-green color-blind users.

## The bee-attracted mouthpiece: an environmental color hazard

Tibor tells this story often, because it captures every lesson of visual design in one example. The device was a tongue-controlled and mouth-controlled wheelchair for quadriplegic patients. A key component was the mouthpiece that the patient operated directly with tongue or lips. The development team chose a color for the mouthpiece during design, and the choice was tested indoors, in an office environment, with recruited users and a structured protocol. Everything looked fine.

The auditor asked one question at the first review. What about outdoor use? The team paused. The use specification had described "use environment" in a single sentence that implicitly assumed indoor conditions. Outdoor use was in scope but had not been decomposed. The auditor then asked whether the chosen mouthpiece color might attract insects outdoors. The team had not considered it. A short investigation confirmed that the color was precisely the range that attracts bees. A patient using the wheelchair outdoors with the mouthpiece near the mouth could, plausibly, be stung on the mouthpiece or near the lips. For a quadriplegic user unable to swat an insect away, the resulting harm was not trivial.

The fix was twofold. The mouthpiece color was changed to a hue that does not attract bees. The use specification was expanded to explicitly include outdoor use scenarios with environmental hazards enumerated. Both changes passed through the risk management file and the usability file in parallel. The lesson for every reader is that a color choice is never purely aesthetic, and a use specification that does not decompose the use environment in granular detail will miss exactly these hazards.

## A worked example: a home-use phototherapy lamp

Consider a Class IIa phototherapy lamp for home use. The device has three indicator states: ready (green), treatment in progress (blue), fault (red). The engineering team uses three LEDs and nothing else.

The use specification written from first principles would identify several realities. The user is a lay user, possibly color blind, operating the device at 7 a.m. in winter with sleep inertia, in a room with low ambient light. The user may wear tinted glasses. The device sits at eye level, so glare matters.

Hazard-related use scenarios follow. A color-blind user cannot distinguish red fault from green ready and starts a treatment session during a device fault. A user in low morning light misreads the indicator. A user with tinted lenses sees blue and green as almost identical.

The risk controls combine channels. Each LED is paired with an icon: a check for ready, a sun for treatment, a cross for fault. The fault state adds a short text line. The formative evaluation includes two participants with confirmed color vision deficiency. The summative evaluation confirms that none of the recruited users misidentify the state. The notified body traces color choice to hazard scenario to risk control to residual risk. The design ships.

## The Subtract to Ship playbook for color and visual design

Treat color as a risk control from day one. Before the industrial designer commits to a palette, the usability team writes a use specification that describes the user, the environment, the lighting, the distance, and the physical constraints. The palette is then chosen in service of the hazard-related use scenarios, not the other way around. This sounds slow. It is faster than the alternative, which is discovering during summative evaluation that the palette fails and having to re-tool.

Pair every color with a second channel. If the team cannot explain the device state without looking at color, add an icon, a shape, a text label, or a position cue. The rule is not aesthetic; it is a hard requirement that falls out of MDR Annex I §5 and §22.

Test the visual design with at least one participant with color vision deficiency during formative evaluation. Recruiting is not harder than for sighted participants and the result saves an entire audit round. For lay-use devices under Annex I §22, this is not optional in any meaningful interpretation.

Decompose the use environment in the use specification. Indoor and outdoor conditions. Daytime and night-time. Bright sunlight, fluorescent office light, candle-dim bedroom. For each environment, ask whether the color-coded information remains legible. Add environmental hazards explicitly, including reflections, glare, and, yes, insects where relevant.

Document color choices as risk controls in the risk file. Each color is a decision, and each decision has a reason that traces back to a hazard-related use scenario. Auditors love this trail because it demonstrates that the design is governed, not improvised.

Avoid fighting convention. Red means danger. Green means ready. Yellow means caution. A clever designer who inverts the convention for aesthetic reasons is generating risk for the sake of originality. There is no scenario in which that trade is worth making for a medical device.

## Reality Check

1. Can you open your technical file and find a document that describes the chosen color palette as a set of risk controls, not as brand guidelines?
2. For every indicator color on the device, is there a second information channel, an icon, a shape, a text line, or a tone?
3. Does your use specification describe the use environment in enough granularity to catch outdoor use, lighting changes, or environmental color hazards?
4. Have at least some of your formative or summative participants had color vision deficiency, and did they successfully interpret every device state?
5. Is every color choice traceable from the usability file to the risk management file to the hazard-related use scenario that justified it?
6. If an auditor asked you why the fault indicator is red and not orange, do you have a documented reason, or only a design preference?
7. Does your device avoid inverting safety color conventions, or does it ask the user to relearn red and green?

## Frequently Asked Questions

**Is there a harmonized standard that lists the official safety colors for medical devices?**
There is no single MDR-referenced standard that dictates a fixed palette for every device. EN 62366-1:2015+A1:2020 governs the usability process that selects colors; EN 60601-1:2006+A1+A12+A2+A13:2024 and its alarm-specific collateral EN 60601-1-8 govern indicator and alarm conventions for medical electrical equipment; safety signage conventions at the European level inform the red-yellow-green-blue meanings used in practice.

**What percentage of users should be assumed to have color vision deficiency?**
Roughly 8% of men and 0.5% of women. For any general-population device, that fraction is too large to design away, and Annex I §22 makes lay-user tolerance a hard requirement.

**Can a startup use color alone if the device is for trained professionals only?**
Even for professional users, single-channel color signals are a weak design. Professional environments include fatigue, dim lighting, and colleagues with color vision deficiency. Tibor has not seen a notified body accept "trained users are not color blind" as a stand-alone argument.

**How does the bee-mouthpiece story apply to a device that is clearly indoor-only?**
The story is about environmental granularity, not about bees specifically. Any device has a real use environment, and any use environment has physical properties that can interact with color. Reflections, glare, overhead light temperature, and wall color all count.

**Do color choices need to appear in the risk management file?**
Yes, when they serve as risk controls. EN ISO 14971:2019+A11:2021 treats every intentional design decision that reduces a risk as a risk control, and every risk control must carry a residual risk assessment.

**Is color coding relevant for software-only medical devices?**
Fully. A Class IIa software device that uses red and green as its only signal for critical clinical values is functionally identical to a hardware device with the same flaw, and the same findings apply under the same standards.

## Related reading
- [What Is Usability Engineering for Medical Devices? A Startup Introduction](/blog/usability-engineering-medical-devices-startup) The parent primer on the EN 62366-1 process.
- [IEC 60601-1-6 Usability Cross-Reference](/blog/iec-60601-1-6-usability-cross-reference) How the electrical safety standard hands off usability to EN 62366-1.
- [Risk Management and Usability Engineering Link](/blog/risk-management-usability-engineering-link) How EN ISO 14971 and EN 62366-1 integrate in the risk file.
- [MDR Labeling Requirements](/blog/mdr-labeling-requirements) The labeling side of visual communication on the device and its packaging.
- [Protective Measures: Guards, Alarms, Interlocks](/blog/protective-measures-guards-alarms-interlocks) Where color-coded signals sit in the risk control hierarchy.

## Sources
1. Regulation (EU) 2017/745 on medical devices, consolidated text. Annex I §5, §14, §22, and Chapter III §23.
2. EN 62366-1:2015+A1:2020, Medical devices Part 1: Application of usability engineering to medical devices.
3. EN ISO 14971:2019+A11:2021, Medical devices: Application of risk management to medical devices.
4. EN 60601-1:2006+A1+A12+A2+A13:2024, Medical electrical equipment Part 1: General requirements for basic safety and essential performance.

---

*This post is part of the [Usability Under MDR](https://zechmeister-solutions.com/en/blog/category/usability) cluster in the [Subtract to Ship: MDR Blog](https://zechmeister-solutions.com/en/blog). For EU MDR certification consulting, see [zechmeister-solutions.com](https://zechmeister-solutions.com).*