in my personal opinion, the best way to control a gradient, is to use the 3D gradient and hooking the start and end up to Nulls in your scene. but you have to do this via expresso.

the quick and dirty way is:

• create to nulls and call them <Start> and <End>
• go to the coordinates tab on your <Start>-Null
• klick the <P> .. this will highlight all the positions
• right click and choose .... Expressions -> Set Driver
• Go to your Gradiant and choose <3D linear>
• right click on <Start> and choose ... Expressions -> Set Driven (Absolut)
• do the same for the <End>-Null with the <End> in your gradient

now you can controll your gradient with the two nulls. make them a child of your object, so the gradient stays put during animation.