Actionscript gradient transition help

i have a movie i’ve been playing around with where the user controls the scene by moving the mouse left or right and it scrolls in the direction

i want to add a seasonal-type effect in the background with gradient tweens, but don’t know how to do it other than manually tweening

basically, i want one long clip that has transitions, so i can move it left or right when needed. hope that makes sense

edit: forgot to add…i want it to be a VERTICAL gradient, going horizontally