The interior side of my brown sunglasses is blue. Do you know what it is?

[Foxhome]

I have Ray Ban rb4085. It's color is brown. When I look at the interior side of the glasses its color is blue. Do you know the function of it?

[Foxpark]

it is a reflective coating that is designed to reduce glare from the sun and filter the light blue that is reflected by the sky and seawater in order to protect our eyes.