I'm new to After Effects and I'm working on a project right now that's basically a simulation of a shadow puppet theater inside AE. I am using some silhouettes(comps) with a backlight to project the shadow over a "piece of paper"(solid) so the camera can look at the sum of all shadows projected upon the paper surface from the other side.
Flow of light
And the idea to use this effect rather than ditching the paper and just showing all the solids with no backlight, is to try and recreate the blurriness of the 3D space projected onto a 2D space, so it looks more natural.
(I figured using a technique similar to Translucent Glass by Video Copilot, that achieves a similar effect, but apparently only works for texts.)
So I don't know exactly how to achieve the translucent effect onto the paper.
You can look for references on YouTube, to know how this theaters work/look so you can get my point.