T, here is what I do:
Track 1 (this will be your graduated filter):
– using insert generated media, create a black to white gradient image
– set composite mode set to Multiply (Mask)
– add a Sony Mask Generator Effect
Track 2:
– insert your footage
– make this a child of track 1
Track 3:
– using insert generated media, create a blue image for your new sky color.
– keep this as a parent track
Now, track 1 is your “graduated filter”. You can adjust the gradient to your liking. The blue (track 3) will show wherever the track 1 mask is black, and your clip (track 2) will show wherever the track 1 mask is white.
Jerry