You know the nail biting conclusion to the classic thriller where some rookie cop is disarming the bomb whilst been coached over the radio by the bomb disposal expert. Well, it’s a good job that cop doesn’t have colour vision deficiency (CVD), commonly and wrongly known as ‘colour blind’.
Let me get this out of the way first. Colour Vision Deficiency (CVD) is what most people think is colour blind; Colour blind is where a person cannot see any colour; they see everything in grey scale. You know, blind as in can’t see and colour makes ‘can’t see colour’. Still, most people outside the field of eye health calls it ‘colour blind’, so I’ll kick my pedantic nerd brain into submission and do likewise. To me, this is like putting ketchup on ice cream – It’s just wrong - but I will have to fight the screaming in my head and will refer to it as ‘colour blind’ in the rest of this blog.
You need to know that Objects don't have a colour, they give off light that appears to be a colour. Yeah, I know that banana looks yellow, but that’s because the rest of the spectrum is absorbed by the banana. You can only see the yellow light reflected back. Well, it’s refracted, but I’m not going to split hairs.
Colour blindness is a decreased ability to see colour, or a decreased ability to tell colours apart from one another. It’s like the average Joe or Jo at a wine tasting session. They’ll have difficulty picking out the 2015 Bordeaux (apparently, it was a good year for French wines) or telling the Cabernet Sauvignon from the Shiraz. If you can’t tell white from red wine, you could be said to be wine blind. Yup, I’ve just made that up, but I like it. Anyway, most of the time, going by the “It’s red and it tastes alright to me” mantra works fine, right up until the bomb goes off.
Each colour on the spectrum has a frequency. That doesn’t mean that it runs to a time-table, it means that it comes in waves of a certain, well, frequency. Ah, but hold on, that’s a bit misleading in that there are no distinct colours in the colour spectrum, despite any assertions in the song. Each colour fades into its neighbouring colour on the spectrum. So, red fades into orange and orange into yellow, but what if there is a little more red than yellow; where is that in the song? So, the frequency is a sliding pitch, like a note starting low and getting higher. The low is the red and the high is blue, if you trust that song. Incidentally, some people perceive letters or smells as colours. If that’s you, then your brain isn’t scrambled; you’ve got synesthesia.
So, that sort of touches on what colours are in about as small a nutshell as I can manage, akin to a pistachio nutshell, me thinks. If you want to know more, you’re more of a nerd than I am and really need to get out more.
Right, here’s a basic biology lesson on the eye. Well, I’m going to skip the lesson on the parts you can see and go straight to the business end. At the back of the eye, we have the retina that contains the cells that respond to light. These specialized cells are called photoreceptors. There are 2 types of photoreceptors in the retina: rods and cones. Rods are the cells that allow us to see dark and light, and shape and movement, but it’s the cones that are going to play a starring role in this blog.
Cones are the cells that allow us to perceive colour. There are three types of cones, each responsible for absorbing blue, red, and green wavelengths in the spectrum. The ones called green cones are most sensitive to green colours. Yeah, no surprise there. The ones called blue cones are most sensitiveto violet colours. Ok, it’s sort of blue. Now this is going to pop your head. The ones called red cones are most sensitiveto yellowish-green. It’s just the way they are. Deal with it and let’s move on.
Black is perceived when all colour is absorbed by an object or there is no light to reflect and so no rods are being stimulated, and white is all three rods getting the hell stimulated out of them. Yes, white is made up of red, blue and green light. I know this is true, and I stand by it, but I haven’t got a Scooby how three prime colours mixed together make white. Well, I have, but I can’t be arsed to go into it here.
The intensity of light can change what colour you see considerably. For example, a low-intensity orange-yellow is brown, and a low-intensity yellow-green is olive-green. Incidentally, isn’t it weird that we can’t see "reddish green" or "yellowish blue"? You’re going to read that sentence at least twice, pause to try and think of something that is that colour, then fight the urge to tell someone your new amazing fact.
Causes of Colour Blindness
In most people with CVD, problems with colour vision happen when one or more of these types of cones are not working properly or just not there. Much rarer, the problem comes from dodgy colour processing in the brain.
Several factors can produce problems with the cones including:
• inherited through genetics (blame your mum and dad… probably your dad)
• trauma (wear your goggles when welding or using power tools)
• exposure to ultraviolet light (wear decent sun-glasses and don’t look at the sun)
• an effect of diabetes (One more reason to eat healthy)
• degeneration with age (…er, not much you can do about this)
With all those causal effects, it’s not surprising that it’s more common than you’d think. Just about everyone knows someone who does not see the world quite like they do because of a form of colour blindness. Oddly, though, it’s much more common in men than in women (read to the end to find out why). The most common type of colour blindness, which is Red–green, affects up to 8% of males and 0.5% of females of European descent. Rest of the World? I didn’t check. Are they using Sky? Nope. Like I say, I didn’t check. Still, that’s a pretty significant portion of the population that we shouldn’t ignore.
Oh, and your colour receptors get weaker and weaker the older you get, so make good colour contrast a standard now and it will be cool when you’re elderly.
What it looks like
Colour blindness can either be partial or total. There are two major types of colour blindness: difficulty distinguishing between red and green, and difficulty distinguishing between blue and yellow.
I don’t want to worry you, but you don’t need to take a colour blindness test to get a driving licence. It’s ok though. Traffic lights aren’t a problem. I bet you’re thinking that they just see the top light is stop and the bottom light is go. Well, that’s what I thought until I looked it up. The reality will go some way to explaining what colour-blind people see.
Let’s look at the most common as an example. People with partial red-green colour-blindness have difficulty discriminating reds, yellows, and greens from one another.total red-green colour blindness sees red and green both as different shades of yellow.
It’s like only being able to distinguish between a sweet and a dry wine, or “It’s a red”. All you need to know when it comes down to it is which you like and if it’s on special offer at Morison’s. Likewise, all a colour-blind person has to learn is which colour they see relates to which actual colour, just as those without colour blindness learn as a kid that the sky is blue, the grass is green, and the apple is red. Blue sky – Yeah, right. Whoever came up with that didn’t live in the North.
Remember that dress that went viral a few years ago? some saw it as white with gold lace, while others saw it as blue with black lace. Did it matter to anyone but the bride who was wearing it? No. Whatever colour you saw works for you. Same thing with traffic lights.
Some people with colour-blindness just need more of the damaged colour in the mix. For example, with blue-green colour-blindness, to see pink requires a bit redder in there than you’d expect. So, if you’ve got a friend who likes to dress in bright, bold colours now and then, it might be that they don’t actually see it as bright and bold. Go on, I dare you to tell her that she might be colour-blind.
What We Can Do
Here are some things you can do to make your websites and apps more accessible to people with colour blindness.
While the following tips aren’t exhaustive, they do cover the majority of problems colour-blind people experience.
• Text Contrast
To make text readable, it must have a contrast ratio of 4.5:1 for normal text and 3:1 for large text (14 point and bold or larger, or 18 point or larger).
Use a colour contrast wheel or colour contrast checker to make sure you hit this ratio.
• Text overlaying images
Good contrast on text overlaid on imagery, such as sub-titles or captions, is not always easy because some or all of the images may not have enough contrast to the text.
One thing you can do to make the text easier to read is to reduce the background opacity to increase the contrast.
Alternatively, you can style the text itself to have its own solid colour background or a drop shadow.
• Don’t use colour-specific instructions
When designing forms, for example, don’t use colour only to show required fields. It’s best practice to use a symbol cue like the asterisk.
A similar example would be telling a user to click a green button to complete a function. To avoid confusion, consider using size, placement, boldness, contrast, borders, icons, a little green elf waving a flag, and anything else that will help.
Oh, and if you’re a bomb disposal expert, tell the rookie cop to cut the wire on the right rather than the red wire, and hope that they can tell their left from right.
• Give Form Placeholders a Label
A placeholder usually lacks sufficient contrast for the placeholder text. Always use a placeholder label in combination with good contrast.
• Describe the Colour
If it’s relevant, as in, “Do I really want to buy a diarrhoea-coloured iPhone?”, reference the name of the colour in the description of the product, as in ‘Red iPhone 12’.
Using abstract colour names, like sunset yellow can be just as confusing as not using a colour name at all. I’ve seen sunsets that range in colour from yellow to purple. And while we’re at it, exactly what colour is the hair dye ‘Bicycle Yellow’? Stick with hue names as much as possible.
Giving a colour description in text benefits people with normal vision too. For example, black and navy are difficult colours to differentiate on screen, particularly if you’re on a mobile phone in bright sunlight. A text label takes the guesswork out of it.
• Alert Messaging
I’ve only just found this out: Success and error messages are often coloured green and red respectively. Obvious to everyone who hasn’t been blind for the last 25+ years. Using prefix text such as “Success” or an icon makes it quick and easy to read. This is also incidentally useful for a screen reader too – They’ve also been blind for 25+ years.
• Contrast in Graphics
When designing things like graphs, charts, maps and infographics, don’t rely on colour coding alone. Try to use a combination of colour and pattern with, where possible, text description within each segment, then reflect this in the key or legend. For example, combine a red background with a crosshatched pattern, or a blue background with a dotty pattern.
Colour Combinations to Avoid
The following colour combinations should be avoided where possible:
• green/red (Your mother was right – Red and green should never be seen)
• green/brown
• blue/purple
• green/blue
• light green/yellow
• blue/grey
• green/grey
• green/black
Opposite to Colour Blind
the genes for colour are carried on the X-chromosome. Women have two of them, but men have an X and Y chromosomes. This means that women have twice the chance of carrying the right cones as men, which is why more men have colour-blindness.
In rare cases, the XX- chromosome can also result in two copies of a cone, both at slightly different wavelengths. So, for example, a woman with double green cones would see in blue, red and two wavelengths of green. She would be able to make out more subtle differences in green coloured things than other people. So, fella’s, when she tells you that the tie doesn’t match the pocket square, she might know what she’s talking about. Still, no-one but her will care, so go for it anyway.
You think we’re at the top of the evolutionary tree? When it comes to colour vision, even the woman with extra cones doesn’t have a patch on fish, birds and even insects. They see the same colours as us but can also see ultraviolet and infrared. They can’t tell a 2015 Bordeaux from a Buckfast though.