Here is a simple example of line plot without specifying colors using the Matplotlib library.
Changing the line color
We can specify colors for each dataset that we plot with the c=color parameter. (e.g. c='red')
Changing the theme
Matplotlib comes with different themes that you can chose from
Here is a practical example of changing the matplotlib theme.
As you can see we just changed the theme of our plot.
Here you are ! You now know how to change both the color of your plot and its theme.
More on plots
If you want to know more about how to add labels, plot different types of plots, etc... checkout the other articles I wrote on the topic, just here :