Material mask based on overlapping objects in scene?

I’m making a character based on a concept by Toby Allen (link to image attached below) and in the image the character holds a piece of glass that changes the color of the parts of the character that is seen through the glass but not the color of the background.
I thought this effect would be fun to create but I’m not really sure where to start. I’ve been researching Custom Stencils and Custom Depth Pass, among some other things, but haven’t found something that I know how to utilize to achieve the desired effect.
What I basically want to do is to create a mask based on what parts of the character is rendered behind the glass, and then use that mask to lerp between two textures in the character’s material (so that the glass is still rendered on top of the character). And I would like this mask to update in real time so that you can view the character from different angles.

Any tips on how I should go about doing this?
Thank you!

Concept reference:

Character in UE4: