Protects contents from damaging light
I keep these by my sink - one with white vinegar and one with hydrogen peroxide, for disinfecting surfaces (especially wooden or bamboo cutting boards).  Turns out, if you use first one, then the other, they mix on the surface to make a pretty darned effective disinfectant, with really benign impacts on humans and the environment.  Because the bottle is dark amber, it gives the hydrogen peroxide some protection from light - especially since I use it up so quickly.
Rating: 4 stars