Question

why silver bromide is stored in a dark brown colored bottle

Answer 1

In the presence of sunlight, silver bromkde undergoes photo decomposition to result in the formation of silver and Br2. So they are stored in dark bottles to prevent photo decomposition from taking place

Answer 2

Silver bromide used popularly for photographic purposes tends to decompose when light falls on it.
In order to prevent this, dark colored bottles are used as they restrict the amount of light entering the bottle.

Hope it helps ya