After it's done creating the rainbow, it will interact to your mouse and the space key. To show the variables that you can change, move your cursor to the left hand side of the screen.
This was originally a contest with another scratcher but I decided it was good enough to share. All of the code is mine, though. 10/25/14 added modes 11/3/14 added dot size & added tool bar & 415 views! Thanks guys!