,Brightening a Material that is further from camera?

Hello! I hope this isn’t too complicated.

For simplicity, I have 4 boxes in a scene.

2 in front. 2 in the back.

All four are using the same material.

I would like to set something up where the 2 in the back have a parameter that could let me edit it’s color/value based on camera position. Or based on just being behind the front two boxes.

I’m kind of stumped and would appreciate any help. Thank you!

Like this:

You can’t make white brighter than white, that’s why I used the emissive pin:

EDIT: And here’s white at 1500: