Have you ever seen a "one way mirror" (like they use in cop shows) or mirror sunglasses?

To the outsider, it looks like an opaque surface. To the insider, it looks transparent.

I own a pair of mirror shades that appear to be mirrored bright blue, but when I put them on... seeing out, it only appears that my field of view is just a little dimmer (to blot out intense sunlight).

http://science.howstuffworks.com/question421.htm

The AT-AT windshields may be a similar thing. Since we aren't up super close, we may not see the reflection effect on the outside's red eye thing.

Or perhaps the red "Eyes" are not the same as the viewport that the Stormtroopers and General Veers are looking out from... are we even sure about that?

I just think it would look crappy to make all those interior scenes visibly red tinted and just isn't necessary.