Marine modeller. Depends on how old you want the vehicle to be depicted. The original LVTP7 and 7A's had vision blocks with a greenish tinge. Plenty of pics to show that the AAVP carried these over. Even with the hatch down, you could easily see through them so I would definately drill out and replace.
I have a LVTP7A waiting to be finished, and I have drilled out all vision ports. I intend to make replacement blocks from clear casting resin. I have made a little master that I have stuck into some silicone on an old cd case. The intention is to make several of these little moulds and then pour the resin into them. When dry, paint the outer edges black where they fit in the vehicle block frame, then colour both faces with a thinned mix of Tamiya clear green, with a dab of clear blue added.
Later models had a darker smokey brown colour, and apparently as Arty says, the latest have a red tinge.
Here's a pic from the http://afvinteriors.hobbyvista.com/lvtp7/lvtp7b.html page. Notice the blocks on the left.
If you want others, drop me an email.