Reverse mode was added to Cheese Jump in Beta 1.1.3 by Seth and hasn't changed since.
In Cheese Jump, if you type "R, E, V, E, R, S, E", you will go into reverse mode. While in reverse mode, all of the colors change to their reverse colors, and the controls are swapped. (A = Right, D = Left, etc)
All reversed colors are mentioned in their respective articles.