Trying to get consistent transparency/opacity when editing sunglasses

[QuenIgni47]

So basically, I'm trying to do a simple recolor of a pair of sunglasses in the game to give the lenses a nice lightly tinted (so I can still see my character's eyes) red color, and I've managed to do so except for one problem. Whenever I'm outside in the daylight, and my character is facing the sun, and the light actually hits the glasses, the transparency of the lenses are perfect to me. But it's when I'm inside or in a shaded area, or even facing away from the sun, that the lenses become almost completely opaque. What can I do to the sunglasses' lenses to make sure they have a consistent transparency in different light settings? Would this be something in the material file, or the Nif file, or something else?