Go to the screen where you enter your cheats and enter the following code:

Green, Red, Green, Yellow, Green, Blue, Green, Orange, Green, Blue, Green,
Yellow, Green, Red, Green, Green and Red, Red and Yellow, Green and Red,
Yellow and Blue, Green and Red, Blue and Orange, Green and Red, Yellow and
Blue, Green and Red, Red and Yellow, Green and Red, Green and Yellow.

This code will make the Gems (the colored notes that you have to play) really big. It look really cool. Note: In the code it says "and" in the middle of two colors. For example Red and Yellow you must press those two notes at the same time then strum how you regularly play the note when entering cheats.