Easy, and not so easy.
If you subscribe to adobe CC, you can download speedgrade, kind of a movie version of photoshop.
But you'll need to learn the basics of speedgrade also.
In a few words... Add an adjustment layer above all you clips in PP. In the menu choose "send to speedgrade". This will open your PP timeline in SG. Add a key frame in the grading layer for each color adjustment in the correct position on the time line. With the play head parked on the key frame, make your color change for each key frame. When done, click the mouse on the end key frame and an arrow will appear between the key frames. This indicates that the effect will ramp from one key frame to the next.
When done, select save, then and back to PP.
I can't write a manual here, so you'll need to do some googling to learn some more basics about the software.
Good luck!!!
