Histogram bars are differentiated by borders, but right now we can't see any borders on our chart. They're there, but the border color is the same as the bar color. This is a problem; if the bars don't differ in length, we can't separate them visually. (See the last two bars as an example; as they are now, they are indistinguishable.)
Let's fix this by changing the border color. You can also change the color of the bars to make them stand out from the rest of the chart. By doing this, we will make the bars easier to read and the chart more pleasing to look at.
To change the color of bars and bar borders, we add two more arguments to
geom_histogram(), as shown below:
+ geom_histogram(breaks = some_parameters, col = "your_color1", fill="your_color2")
The fill argument sets the bar color, and the col argument sets the border color.