You need to gel the windows so the color of the light coming in matches the tungsten lights that you're using inside.
You need it to look good, as if it hadn't been gelled at all, with no big ripply reflections of the interior lighting.
You need it to stay up for a while, like weeks or months?
Then this instructional is for you. This is the technique used on most of today's top reality shows, where the lighting crews need to gel out whole houses for extended timeframe shooting. As seen on Top Chef, apprentice, She's Got the Look, Jersey Shore, Work of Art, and many others