Sorry if this one already known - I have had a little search in the forums.

On the color gradient fill under effects.

If you have a couple of "keyframes" on the gradient. (lets assume we have 4, 1 far left, 1 far right, 2 in middile.) You can drag the right of the pair, over and past the left, and it is happy. But you cannot drag the left ones to the right.(over/past the existing other keyframe.) Easy to show, a little hard to explain