So definitely try to code a program that do what I described in my previous post.
A hint: you will need to create a global variable, let’s call it step that will keep track on which step of the program you currently are. step = 1 would be red background step = 2 would be green and step = 3 would be blue.
Now the keyPressed() event can change that step variable. And the draw function can use that variable to know wich background to draw.