Why are beer bottles green or brown?

Reasons of why beer
bottles turn green or brown-

Earlier beer was kept
in transparent glass bottles. But it can be seen that during the day sunlight
and UV rays cause chemical reactions in beer to increase the bad smell.
Therefore, alternative measures have to be thought of to protect the beer from
the effects of sunlight and UV rays. This led to the use of brown coating on
clear glass bottles. This brown coating protects the beer from the effects of
UV rays.

Now the question is, if
the problem has been solved in the brown bottle, then why is there a need for a
green bottle?

Between 1940 and 1945,
beer was sold in green bottles. During World War II, the supply of brown
bottles became very tight. As a result beer was sold in green bottles instead
of brown bottles.