Erases everything on the screen. If you pass it an optional color, it also fills the background with that color.
Here's a little drawing program. Drag to draw. When you tap the bomb, everything you drew is cleared.
Here's an example of resetting the screen with a specific color. Run the code, then tap the screen to reset.
You can also pass in three number values for the red, green, and blue color you want to fill the screen with. Each number must be between 0 (for none of the color) to 255 (for all of the color). Run the code, then tap the screen to reset. Experiment with the three numbers to see what colors you can create.