First of all: Don’t bump after only waiting 20 minutes or so, it takes a couple of days to get good replies on here 
As for the color mechanic, I can’t see an easy way to implement it. You can’t really return the color of a material by doing traces. You may however be able to trace out, get a material and then get the material parameters and figure out the colour that way, but obviously it won’t be the same for each pixel, and I’m not even sure if traces can do that alone, probably not without some extra help. Then, there’s the matter of perspective, you’ll have to figure out what direction the camera is in relation to the two objects camouflaging each other, and ensure you cast traces in the right direction.
Another method, is rather than use the materials, just give each blueprint a Variable ‘Colour’. You can find the object with a trace and get that variable, then determine if you should camouflage the object or not. That would require adding a variable to every object in the scene though, which will get a bit out of hand.
The only other thing I can think of is some kind of advanced edge-detection material, but no idea how to really implement that.
In short, it’s far from an easy thing to do. If you’re not sure how to flesh out any of these ideas in a Blueprint, I’d abandon it for now and come back to it at a later date. It’s an interesting idea nonetheless.