Colour Vision Deficiency (Dichromacy) and Driving Licence Classes

Colour vision deficiency, also called dichromacy, and driving licence classes are connected in a way that surprises many people, because the answer is not a simple yes or no. About one man in twelve and about one woman in two hundred has a colour vision deficiency, and most of them have no idea until a test finds it. For a car licence, it usually does not matter at all. For a lorry or bus licence, it can matter a great deal, and for some jobs it can matter even more. This guide explains what dichromacy is, how it is tested, which licence classes are affected, and what to do if your result is not what you expected.

You will learn the difference between the types of colour vision deficiency, how the Ishihara test and the other tests work, and the rules that apply to each licence class in Germany. You will also find out what happens if you fail the colour test, whether there are ways to pass it, and how people with a colour deficiency drive safely every day, because they do, in large numbers. The colour test is one small part of the eye examination, and understanding it will take much of the worry out of it.

What dichromacy is

Colour vision deficiency is usually inherited, and it means that the light-sensitive cells in the retina, the cones, do not work in the usual way. Most people have three types of cone, for red, green and blue light, and the brain compares their signals to produce colour. In dichromacy, one type of cone is missing, so only two types are present. The most common form is red-green deficiency, which affects the red and green cones, while blue-yellow deficiency is much rarer. The most common types are protanopia, where the red cones are missing, and deuteranopia, where the green cones are missing, and there are also milder forms, protanomaly and deuteranomaly, where a cone type is present but works weakly. Dichromacy is not the same as seeing in black and white: very few people have complete colour blindness, and most people with a deficiency see colours, just not the same colours as everyone else.

The effect on daily life is usually small, and many people never notice it. Reds and greens can look similar, especially in poor light, a brown may look green, and a red traffic light may look orange, but other clues help: the position of the light, its brightness and its shape. Most people with a deficiency learn the traffic light order early on, red at the top, amber in the middle, green at the bottom, and the traffic light is only one of many cues on the road. For a car driver, that is usually enough. For a professional driver, who must respond quickly to coloured signals, coloured wires and coloured markers, the rules are, quite understandably, stricter.

How the colour test works

The most common colour test in Germany is the Ishihara test, named after its Japanese inventor. You are shown a series of plates, each with a circle made of coloured dots, and inside the dots there is a number, or sometimes a path, made of dots in a different colour. A person with normal colour vision can read the number clearly. A person with red-green deficiency sees a different number, because the colours that make it up are hard to tell apart, or sees no number at all. The test usually uses between twelve and thirty-eight plates, and you need to read most of them correctly to pass. It is quick, painless and standardised, and you can try a similar test at home with our colour vision test tool, although the home version cannot replace the official test.

If the Ishihara test is unclear, there are other tests. The anomaloscope is a device in which you mix red and green light to match a yellow light, and the result shows exactly what type of deficiency you have and how strong it is. The Farnsworth test asks you to arrange coloured caps in order, and it measures how finely you can sort colours. For driving licences, the Ishihara test is usually enough, and it is the test most opticians and doctors use. The result is not a judgement on your driving, it is a measurement of your colour vision, and it is recorded in the same way as your visual acuity. If you fail it, the examiner will tell you so, and the next step depends on the licence class you want.

Which licence classes are affected

For the car licence, class B, a colour vision deficiency is not usually a barrier. The German driving licence rules do not require normal colour vision for a private car licence in the same way that they require visual acuity, and a driver whose colour vision is weak can still drive a car, provided the rest of the examination is passed. That is the position for most countries in Europe, because traffic lights are standardised by position and because colour is only one of the signals on the road. If you hold only a class B licence and you discover a colour deficiency at the eye test, the usual outcome is that the licence is granted anyway, and you drive as normal, with the knowledge that you should be particularly careful with coloured signals at night and in bad weather.

For professional classes, the position is different. For classes C and D, lorry and bus, the medical examination includes a colour test, and the rules are stricter: the examiner must be satisfied that you can distinguish the colours that matter for safe professional driving, including the colours of traffic signals, signs and warning lights. A mild deficiency may still pass, especially if the anomaloscope shows that you can distinguish the important colours, but a strong deficiency can lead to a refusal, or to a restriction. Some other licences, such as the taxi and passenger transport licence and the driving instructor licence, apply the same stricter standard. If you are applying for a professional class, it is worth finding out where you stand before you pay for the driving school, by asking the optician or the doctor for a colour test first. Our article on colour vision in road traffic covers the practical side of driving with a deficiency.

Passing, failing and borderline results

The Ishihara test gives a clear result for most people, but not for everyone. A small number of people are borderline: they read most of the plates but miss a few, or they miss the same plates every time. In a borderline case, the examiner will usually do more testing rather than record a failure, either with more plates or with an anomaloscope, which measures the deficiency precisely. The anomaloscope result is expressed as a range, and a mild range can be enough for a professional class, while a wide range cannot. It is a fairer test than a simple pass or fail, and if you are borderline, it is worth asking for it, because it may be the difference between a refusal and a licence.

There are also practical factors that can affect the result. The Ishihara test must be done in good daylight or under a standard white light, because a yellow or dim light changes the colours of the dots. The plates must be clean and not faded, and you should be wearing your usual glasses or lenses. If you take the test with a cold or while taking a medication that affects vision, the result may be different from your normal result. There is no way to prepare for the colour test in the sense of improving your colour vision, and you should be wary of any product that claims to do so: coloured glasses that promise to fix colour vision can change how the plates look, but they do not change your colour vision, and the examiner will not accept a result obtained with them.

Driving safely with a colour deficiency

Millions of people with a colour vision deficiency drive safely every day, and they do it by using the cues that are always there. Traffic lights are the classic example: red is at the top, amber in the middle, green at the bottom, and their brightness and position identify them even when the colours look similar. Road signs use shape and symbol as well as colour, and the signs that matter most for safety, such as stop signs and give-way signs, are identified by shape before colour. At night, the colour of a light is less important than its position and whether it is on or off, and in fog or rain, everyone is relying on position and brightness rather than fine colour distinctions.

There are a few extra habits that help. Learn the position of the lights on a new route rather than relying on their colour, keep a greater distance from the car in front when the light ahead is hard to read, and if you are unsure at a junction, wait for the traffic around you to move rather than guessing. If you drive a lorry or bus professionally, tell your employer about the deficiency, because there may be signage or equipment in the depot that uses colour alone, and a small change, such as labelling a coloured wire, can make a real difference. The deficiency itself does not make you a bad driver: it makes you a driver who should use all of the information on the road, not just its colours.

The medical route and assessment if refused

If the colour test leads to a refusal for a professional class, there are still steps to take. Ask the doctor or the examiner for the result in writing, with the anomaloscope measurement if one was done, because that is the document that any appeal or assessment needs. The next step is usually a specialist examination by an ophthalmologist who works for the driving licence authority, or a formal medical assessment at a centre that tests driving fitness. In that assessment, the question is not whether you can read Ishihara plates, but whether you can drive safely, and the assessment can include a practical test with real traffic lights and signals, which is a fairer measure of the skill that matters.

Be realistic about the chances. A strong deficiency that prevents you from distinguishing red and green lights will usually lead to a refusal for a professional class, and no assessment will change that, because the safety requirement is real. A mild deficiency, on the other hand, often ends with a restricted licence, for example a licence that allows driving only in daylight, or a licence for a specific class of vehicle, and those restrictions can be a good compromise. Whatever the outcome, talk to the authority rather than to a driving school about the next step, because the authority is the body that decides, and it can tell you exactly which assessment it wants. The assessment costs money and takes time, but it is the correct route for a borderline case, and it often ends with a licence.

Colour vision deficiency: living and driving with it

For most people with a colour vision deficiency, driving is perfectly possible, and the rules reflect that. The tests that matter for a driving licence are the ones that check whether you can distinguish the colours that matter on the road, and those are the red, amber and green of a traffic light, and the red and white of a road sign. A person who cannot tell red from green in an Ishihara test can often still tell a red traffic light from a green one, because the lights are in different positions, and because their brightness differs. What is harder is a situation where colour alone carries the information, such as a coloured line on a map or a coloured warning on a dashboard, and that is why the ophthalmologist’s report looks at the whole picture rather than a single test. If you have a colour vision deficiency, the practical advice is simple: learn the positions of the traffic lights, keep your eyes on the road rather than on the colour alone, and tell the examiner if a particular test is difficult, because the report should record what you can do, not only what you cannot.

Frequently Asked Questions

Does colour blindness stop me getting a car licence? Usually not. A colour vision deficiency is not normally a barrier to a class B car licence in Germany, as long as the rest of the eye examination is passed. The stricter rules apply to professional classes C and D.

What is the Ishihara test? A series of plates made of coloured dots, with a number hidden inside. A person with normal colour vision can read the number, while a person with a red-green deficiency sees a different number or none at all. It is the standard colour test for the driving licence examination.

Can I drive a lorry with red-green colour blindness? It depends on the strength of the deficiency and on the test result. A mild deficiency may still pass, especially with an anomaloscope test, while a strong deficiency can lead to a refusal or a restricted licence for classes C and D.

Can colour vision be improved? No. Colour vision deficiency is usually inherited and cannot be changed by food, exercise or supplements. Special glasses can change how colours look, but they do not change colour vision and are not accepted in the official test.

Can a colour vision deficiency stop me getting a licence? For a car licence, almost never: the rules for class B do not require normal colour vision, and only certain professional licences ask for more. What matters is whether you can distinguish the signals that matter on the road, and most people with a deficiency can.

Conclusion

Colour vision deficiency, or dichromacy, is common, it is usually inherited, and it is not the same as being blind. For a car driver it changes very little: traffic lights are positioned by order, signs are shaped, and the roads are full of information that has nothing to do with colour. For a professional driver the rules are, quite rightly, stricter, and a strong deficiency can limit the classes you can hold. The test itself is quick and fair, and a borderline result should be followed up with an anomaloscope and, if needed, a specialist assessment.

If you discover a deficiency at the eye test, do not panic and do not try to hide it. Get the measurement in writing, ask which classes it affects, and talk to the authority about the options. For most drivers the answer is that nothing changes, and for the rest it is a restriction or a different class rather than the end of driving altogether. The plates tell you about your eyes, not about your ability to drive safely.