In Little Big Planet 2, you can pick any color of the rainbow, same goes with LittleBigPlanet 3.
How to Make Gas Really Colorful in Little Big Planet 2
Go to My Moon, open your popit, get any material and place it. Now go to the tools bag, select the gas, and tweak it to any color and 10% brightness.(It looks like that in The Factory of a Better Tomorrow.)