Except for the sky and the ocean/sea, blue is a very rare color in nature. Blue is my favorite color, so I wanted to find out more!
There are very few animals and plants which are colored blue..but usually they are all really great to look at! But are they really blue? For example, butterflies use light to communicate and they display some of the most detailed and varied patterns. These patterns allow the butterflies to communicate...they deliver messages such as "I am toxic", "I am a male" etc. The butterflies' colors come from tiny scales, which contain pigments. These absorb all colors except what we see.
However, most butterflies do not have a blue pigment. If you look from different angles, you will see strange changes in hue. Therefore, in the majority of cases, the blue color comes from the shape of the wing scale itself. The wings are made of many very small ridges which are arranged in a particular way - light waves bounce off of these surfaces. Blue light has just the right wavelength so that the reflected light waves are in sync - so the color blue makes it to our eyes.
This is amazing stuff! Considering that "common sense" would tell most of us that blue is just another color/pigment. While in truth, blue pigments are extremely rare (but do indeed exist).
For more information and cool more in-depth explanations see this video: