CLICK ON EVERYTHING! Even click on the background! You can also use the arrow keys to change the background.
For the backgrounds, please note that the color changes each time you click on them. If you click on them 4 times they will go back to their original colorings. I only made this because I was bored. Also, most credit for ideas/code structure goes to the Scratch team. This is from their tutorial. I only added on to it like a month after I made it.