Rainbows are not an extremely rare phenomenon, even though they feel that way. You would think that because they need sunlight and water in the air in the form of mist, fog or rain, they would be seen more often.
Rain droplets serve as a type of reflector of light. White light enters one individual rain droplet and exits as one specific color of the spectrum. Without millions of such drops, a rainbow is not possible to form. If there were just a few, then there would be a rainbow of only a few colors. This is typically why the meteorological marvel appears usually after a storm.
From Hawaii to Ireland and Brazil, there are many destinations around the world where you can see the beautiful multi-colored arc in the sky. Rainbows create an incredible spectrum of colors; they can turn any average photo into an Instagram worthy picture.