How to design for the colour-blind

Digital Arts | 28 August 13

Image: Dreamstime

A significant proportion of people are colour-blind (about eight per cent of men and half a per cent of women.)  Yet few businesses – both creative and clients – bother to check whether their visual materials are accessible to those who are unable to distinguish between certain colours. 

As a result, these businesses unwittingly frustrate this audience and in many cases prevent them from becoming customers altogether.  Fortunately, ensuring that visual materials are “colour-blind friendly” is easier than one might think.  In this article, we’ll show you how to avoid alienating this audience and losing potential sales.

What is colour blindness?

Colour blindness is the reduced ability to distinguish between certain colours.  It is usually inherited, but can also occur as a result of physical or chemical damage to the eye, nerve or brain.

The most common form of colour blindness is red-green colour blindness (which includes the conditions protanopia, deuteranopia, protanomaly and deuteranomaly).  Blue-yellow colour blindness (which includes the conditions tritanopia and tritanomaly) is another, less common, form of colour blindness.

While a significant proportion of people are colour-blind, very few people cannot see any colours at all. Only a tiny percentage of people have monochromatic vision. The term “colour blindness” is therefore something of a misnomer.

Why bother worrying about it?

There are a number of reasons why so many businesses fail to check whether their materials are colour-blind friendly. In our experience, most fail to do so because they are unaware of the stats.  That is, most businesses simply don’t realise that a significant proportion of the population is colour-blind, so there is an education ‘gap’.  Having said that, we have also found that those businesses that are aware that more than four per cent of people are colour-blind, often do nothing about it, dismissing this figure as trivial.

The reverse is true of course; because while this percentage may sound small, unless your business targets a truly microscopic audience, it actually represents a huge number of people and thus, a massive amount of potential revenue.  But while businesses continue to ignore this reality, this revenue continues to trickle down the drain—ironic, given the current economic climate, that some businesses feel that they can afford to ignore the needs of four per cent of the market.

Add to above the general misconception among businesses that making visual materials colour-blind friendly is a hugely expensive and time-consuming affair—and suddenly they’ve put enough obstacles in their way to ‘feel a bit less guilty’ for not doing anything about it.

Are you discriminating?

Creating content that is inaccessible to the colour-blind may also constitute discrimination.  It certainly contravenes the Web Content Accessibility Guidelines published by the World Wide Web Consortium (W3C;—that is, the guidance that underpins the legislation on web accessibility in many countries. So, the harsh reality is, if you don’t make your content accessible to the colour-blind, you may risk a lawsuit.

How businesses cause problems for the colour-blind

Businesses cause problems for colour-blind people when they use colour alone to convey information. This mistake is most frequently made in relation to the design of maps, diagrams, graphs, charts and other types of infographic.

These problems seem to be made worse when the coloured items are small. That is, some colour-blind people report that they can only distinguish certain colours if they have a sufficient ‘mass’ (for example, they might perceive a thick coloured line as being red, but a thin version of the same line as being black).  This is a possibility rather than a confirmed trait, but nonetheless it’s worth bearing in mind.

A good example of getting it wrong

Websites that have a ‘ticketing’ business model tend to be common culprits of using colour alone to convey information. These websites typically provide seating plans to help their customers choose the best available seats for the event that they are booking. Here’s an example:

Running this particular seating plan through Colsim – our online colour-blindness simulator – reveals that it is unusable for people with protanopia and deuteranopia.  Here’s how it appears to people with protanopia, for example:

Remind us where the seats with a restricted view are again?

How designers can eliminate these visual faux pas

Businesses can eliminate these types of problems by ensuring that any information that they convey though the use of colour is also conveyed via another means. Applying this 'safety net' means that those who cannot perceive the colour can still perceive the information.

Returning to our seating plan example, we could easily eliminate the aforementioned problem by simply adding the letter 'R; to the restricted-view seats.  This would ensure that those who are unable to discern the difference in colour could still make the necessary distinction between the two types of seat.

An alternative solution would be to change the shape of the restricted seats – from rectangles to, say, circles – or to apply a pattern to the restricted seats – such as a stripy overlay – while leaving the presentation of the non-restricted seats unchanged.

How designers can determine whether their materials are accessible to the colour-blind

Running your visual materials through a colour blindness simulator will tell you whether they are “colour-blind friendly” or not. Where they aren’t, you should be able to fix them quickly and easily using one of the simple techniques described above.

How colour blindness works

A normal human retina contains two kinds of photoreceptive cells: rods (which are active in low light) and cones (which are active in daylight). In most retinas, there are three kinds of cones, each containing a different pigment, which are activated when the pigments absorb light.

The spectral sensitivities of these cone types differ as follows: one is most sensitive to short wavelengths within the visible spectrum, one is most sensitive to medium wavelengths and the other is most sensitive to medium-to-long wavelengths, with their peak sensitivities being in the blue, green, and yellow-green regions of the spectrum, respectively. These cones are often called S cones, M cones, and L cones for short (reflecting their sensitivities to short, medium and long wavelengths).

Colour blindness results when one or more of these three cone types are defective or absent in the retina.

Types of colour blindness


Monochromacy, also known as 'total colour blindness', is a lack of ability to distinguish colours. It is caused by the absence or defectiveness of two or all three, of the different types of cones. Those with this condition see the world in shades of a single colour (red, green, blue or grey). It is extremely rare, however—affecting approximately 0.00001% of men and women.


Dichromacy is a moderately severe form of colour vision deficiency, caused by the absence or non-functioning of one of the three types of cones.

Dichromats with protanopia (approximately 1% of men and 0.01% of women) have absent or non-functioning L cones. As a result, they see reds, oranges and yellows as shifted towards green, and as being less bright than people with normal colour vision. This makes it hard to distinguish between these colours. They also find violet, lavender and purple to be indistinguishable from various shades of blue because their reddish components appear so dim.

Dichromats with deuteranopia (approximately 1.5% of men and 0.01% of women) have absent or non-functioning M cones. As a result, they see oranges, yellows and greens as shifted towards red, making them hard to distinguish. Violet, lavender, purple and blue would also appear pretty similar too.

Dichromats with tritanopia (approximately 0.008% of men and 0.008% of women) have absent or non-functioning S cones. As a result, they have difficulty distinguishing between greens, cyans and blues; and yellows and violets. They can also confuse pinks, oranges and browns.

Anomalous trichromacy

Anomalous trichromacy is a mild form of colour vision deficiency, occurring when one of the three types of cones is altered in its spectral sensitivity.

Anomalous trichromats with protanomaly (approximately 1% of men and 0.01% of women) have defective L cones. They therefore experience similar, but less severe, problems to those with protanopia.

Anomalous trichromats with deuteranomaly (the most common form of colour blindness, affecting approximately 5% of men and 0.4% of women) have defective M cones. They therefore experience similar, but less severe, problems to those with deuteranopia.

Anomalous trichromats with tritanomaly (approximately 0.01% of men and women) have defective S cones. They therefore experience similar, but less severe problems, to those with tritanopia.

About Etre

Paul Schwartfeger is MD and Simon Griffin is director of design at Etre, a premium, research-led design firm that takes a unique, people-centred approach to helping its clients innovate and grow. Its clients include American Express, John Lewis, Mars, Rolex, Vodafone, Nokia and Eurostar.


Paul Wallas said: This tool and the Internet Explorer Toolbar (WAT) is a great way of testing your designs for the various color blindness types.