Another important aspect to consider when designing for effective visualizations with color is the effect of size. The size of an object on the screen affects the way the color is perceived. Let me show you an example. So, here in this scatter plot, I have lots of dots and these dots are colored according to a number of categories, these categories that you see on the right. Now, since these dots are very small, it's very hard for you to distinguish between all the different colors. You can maybe perceive the difference for some shades, but you definitely can't distinguish all these categories that you see on the right. Now, if I make these dots bigger, you can see that now, you can distinguish a lot more colors. So, this example gives you a sense of the fact that size interacts very heavily with color perception. And this is something you have always to keep in mind. Very, very important. Let me give you another example, I've taken this example from a very nice tool called Just-Noticeable Differences, which is a library developed by Connor Gramazio, who was a visualization researcher and he's been developing methods to automatically decide how much of a difference is needed in a color dimension so that a difference is perceived, taking into consideration how large the area of this object is. And here, you see that a certain level of difference, for different sizes, it's easier or harder to perceive the difference. So, the elements in the first row, the difference can be perceived very easily. The one in the middle is a little harder, and the one at the bottom is very, very hard. So, here is another example that clearly shows you how size affects color perception. So the general rule for visualization design is that when you have small areas, you should try to have colors that have high saturation. And when you have large areas, you should try to have callers who have low saturation. I think another rule that you should consider is that if you want people to be able to distinguish between a certain number of colors, the objects can't be too small, okay? So let me show you what happens when you have large and small areas. I created these examples using a tool that is called ColorBrewer, that I'm going to introduce in a moment. And as you can see here, when we have large areas, if we have colors that are too saturated and too bright, they tend to create clutter and too strong visualization. We have what is called vibrant colors that stimulate our vision too harshly. On the right, I have exactly the same representation but with colors that have a much, much lower saturation, and because of that they are not as aggressive as those ones that you see on the left. So, as a general rule, it's important when you have large shades of color, large areas, not to use colors that are too saturated. The opposite is true for small areas with colors that need to be perceived across very small objects. This is what you see on the bottom left of the same image. It's much better to have highly saturated colors when you have small objects.
