Why are Beer Bottles Brown or Green?

When beer is stored in transparent bottles, sunlight penetrates into the bottle and leads to the decomposition of some structures inside the beer that has been exposed to sunlight for a long time. As a result of these reactions, the taste of beer deteriorates, and it starts to smell "skunky," therefore, beer taste is characterized as the smell of a skunk. 

 The sensitivity of beer to light is the reason for a critical, challenging shelf-life problem for the beer industry and is the main reason for storing beer in dark-colored containers.