To simply change the background color of your canvas or Page follow the instructions in this image.  Very simple to do.   However....If you want to change the color of the background with an image in it Read on:

I prefer to make the image a PNG then select a background, add the background to your canvas, Then add your image!  

Here is a Video to change Backgrounds to Textures, Clouds, Water, Etc!                           Just Click Here!