Global key frame is for post-processing and overall effects.
1.Click the “Global” button and set the saturation to 2, then register a Global keyframe at frame 0 on the timeline.
2.Next, Set the overall saturation to 0, then open the sky panel and reduce the overall shadow brightness，and register a Global keyframe at frame 41 on the timeline.
Finally, the animation of overall color change from frame 0 to frame 41 is completed.
All the properties in the sky panel and all the properties in the post-processing panel can be animated in this way by KEY frames.