Sunglases

There are two types of sunglasses. The first regular type is just colour-tinted, and the other type looks like colour-tinted mirrors.

1° The first type of glasses seem to have the same colour on both sides of them. This type is like an absorbent filter; it transmits light of a certain colour, e.g. green, and absorb other colours.
2° The other type uses a completely different phenomenon - it reflects a given colour. As a result, a pair of glasses which look red may reflect red colour so that you don't see red when you wear them. The world observed through such glasses lacks red, and there is much more blue in it.

They are so called reflecting filters. The front surface of the glass is covered with a thin selective reflection layer. A similar thin layer covers your computer screen.