Tracking mask in Davinci Resolve Video editing n00b here. I have a clip where a person touches a screen with an access card. I want the screen to be red before it is touched, and green after.

I've used a PlanarTracker node to track the screen, and Corner Pin to place either the red or the green overlay on top. This part works fine.

The problem is that the person's hand and the access card cover part of the screen for a few frames, but the colour overlay is always on top of the hand. I think I need to add a mask to the PlanarTracker that follows the card and the hand, but I don't know how to create this mask.

I tried adding another PlanarTracker using the original clip as input, tracking the card, and connecting the output to the mask input of the first PlanarTracker, but this doesn't seem to do anything.

Any suggestions? What am I doing wrong? Should I follow an entirely different approach?
I don't know the footage, but would guess that it isn't good enough for tracking.
In this case, you will need to Rotobrush it. Or manually create a mask. If it is only for a few frames and a smaller part of the screen, I guess a rough mask with a bit of a higher edge blur will do the trick.