Are we really sure it is an EO/IR window? Or could it not more likely be some sort of dielectric panel/array?
At least on this latest image it does not look like glas.
I'm guessing they maybe protective cover, or maybe like early J-20 prototypes just a non transparent place holder for now
edit: another possibility is that the coatings reflection just happens to be in this color viewed from this angle, need more pictures from different angle to see