How to match foreground and background?

If you track the camera, the horizon will be a long way away from the camera so that is probably impractical. On the other hand, if the Camera Tracker solves the shot as a Tripod Pan, you can probably use the Camera Tracker to replace the horizon and sky.

I've done this before by motion stabilizing something on the horizon using the AE tracker. When you get that spot to stop moving you can by Motion Stabilizing a single point, you can add your mountain shot to the background, add a null to the comp, reveal the Anchor Point property of the Drone Footage layer and the Position property of the null and then tie the null's position to the animated Anchor Point motion stabilizing added to the footage. The last step is to move to the first frame of the comp and parent the mountain layer and the drone footage to the Null. This will remove the motion stabilizing from the drone shot and add the motion to the mountain layer. It may also take a couple of keyframes on the replacement layer to complete the illusion of accurate parallax shifts.

If all that fails, you can try motion tracking something on the horizon and then setting the mountain shot as the target for the motion tracking.

If you don't want to experiment with all of those methods then post the video so we can see what kind of move the camera makes and we can give you some pointers.

Lumetri Color effect would be good to control color. You see the link below to get the idea of Lumetri color.

https://helpx.adobe.com/after-effects/how-to/repair-video.html