GRAPHS IN COLOR
Usually, I am against using much color in the graph following the rule: make it work in black and white first. This rule helps simplifying your graphs and avoid clutter.
Contrary, if I have to chose between using color or shape I always pick up color. It is a much stronger visual clue and human eye identifies its distinguishes it much easier.
So, following this rules I am going to transform this graph from Sung et al. 2016 into a more readable graphic:
Authors chose two ways of categorizing their data: a shape and grey scale. Therefore the first step is to simplify and as mentioned above first make it in black and white, here is the result:
I also removed the extra lines in the background making the whole image much clearer and driving attention to actual data. As you can see this way the graphic still work, so how about adding some color?
Doing so, is actually quite tricky and I would advise giving it some thought. Usually first pick would be to use red and green:
Looks nice, doesn't it? The only problem is that it will turn out difficult to read for color blind. Illustrator allows you to check for it, so you can see that red/green graph appears as follow:
One of the options is to shift away from the red into a more orange color:
The other option is to go for blue rather than green:
This last one is my personal favourite, as not only it work well for colorblindess, but as colors differ in lightness once they are printed in black and white none of the information is lost: