By far, the most common type of color blindness is the one that is due to
the lack of medium and long wavelengths.
This is by far the most common.
And in turn, this means that
the most common type of color blindness is the one in which it's
hard for color blind people affected by
this type of color blindness to distinguish between red and green.
So distinguishing between red and green is by far
the most common problem
in visualization and in general graphic design when you are using color.
So now, I'm going to show you a few examples that I've taken from
a blog post in the website of Tableau Software,
and it's titled Five Tips on Designing Colorblind-friendly Visualization.
And here, there are examples of how some color pallets that are used and have been
designed to be used in Tableau appear when two people who are normally sighted,
and to people who have some form of color blindness.
So, a very common problem here is the one that happens when you are using green and red,
and a common type of
color palette that people use is what is called the Traffic Light Palette.
And this is often desired because people think that it's intuitive,
and because of that,
it's easy to interpret.
But as you can see,
on the right-hand side,
all these colors are very,
very hard to distinguish for a color blind person.
This is another one,
it's a color palette that is called Tableau 10 Medium,
that is one of the standard color palettes available in Tableau.
But again, if you see the same palette,
when it's transformed in a way to see how
a person with color blindness would perceive it,
you can see that there are many colors that can't really be distinguished.
So for instance, it's very hard to distinguish red from green and brown.
It's very hard to distinguish between blue and purple,
and it's very hard to distinguish between pink and green.
So, this is clearly a problem if you want to create a visualization
that can be perceived by a person who is affected by color blindness.
So, now, the next question obviously is,
how do you design visualizations that are safe for color blind people?
That color blind people can read safely?
So, there are a number of things you can do.
Here is another color palette, again,
that is available in Tableau software and it's been explicitly designed to
be effective also for people affected by color blindness.
So there are a couple of things here.
First of all, if the difference between the colors
is due to the difference between blue and red shades,
in most cases, these can be distinguished.
Another thing that can be done is,
you have to remember that color is a three-dimensional object, okay?
So, not only we can vary color hue in colors,
but we can also vary the color intensity or lightness and the saturation.
So in general, if you want to create
a color palette with different colors that can be used with color blind people,
you can also play with the color intensity,
and this is exactly what is done in this color palette, okay?
Of course, these clashes with another constrain or need that you may have,
when you're using categorical color palettes that you don't want
one color to stand out compared to another one.
And this is a trade off.
You can't really solve both problems at the same time.
Another thing that you can do when you design a new visualization is to
check out how this visualization is going to look like to people who are color blind.
And to do that, there are a number of available tools on the web.
Here, I'm showing you one of the many who are available.
This is called Vischeck.
And in Vischeck, you can upload an image that you saved on your computer,
and see how it looks like to different types of color blind people.
So, here is an example.
On the left-hand side,
you have the original image,
and then you have on the right,
two images created by Vischeck to show you how they look like to color blind people.
So, this concludes this part about color blindness.
I just want to briefly summarize what you can do.
So, the first thing you can do and probably the safest one is to use palettes that have
been explicitly designed by someone who is an expert to be used for color blind people.
Another idea is to use the range between blue and
orange or blue and red because this one is normally safe,
at least for a large percentage of color blind people.
The next one is to consider color variations on
the axis of color intensity and/or saturation.
And the last one, by the way,
I think you should always go to this step when you are designing for color blind people,
is to test your design with one of
the many available tools that transform an image into a mini-image,
simulate how the image would be perceived by a person who is color blind.
