There are a number of ways to change colors of graphs. Whenever the graph is created, you can right click on the space and you will have to option to change color. If you want to change the color of distributions forever, go to Preferences>Platforms>Distribution, select the Histogram color box and select the color you want. In preferences there is also the option to change graph background colors in the Colors section, see below
Screen Shot 2020-08-19 at 12.43.22 PM.jpg
"All models are wrong, some are useful" G.E.P. Box