These are vehicle I.D. pannels that reduce the thermal signature in the spot that is covered. So if you were to look through a M3 thermal that is set on "Black Hot" , meaning every thing that is hot will show up in black, there will be a white square. And if you are set on "White Hot" it would be the opposite. We use these pannels to reduce as you said the Blue on Blue or the Friendly Fire.
They work for the most part and they are better than nothing. In my HMMWV Scout Platoon we have them mounted on the hood and both front doors.
A big problem that still leads to friendly fire is the lack of cross talk between units on the battle field or guys getting lost and being out of their sector. Another big problem is that we have these awesome weapons like the M1 and the main gun can shoot farther than the sight can see clearly.
The bottom line is that you better know where you are and you better know where all your buddies are. And you better be able to talk to them.
Building the pannels for a model should be easy if you use Evergreen styreen sheets. I don't know the exact size off the top of my head but they are about a 3' X 3' square. They cover the whole width of a HMMWV door.
Hope this helps,
Pat