"Feeling Blue" under "Blue Sky"

"Blue Sky"  Can we say "blue" is the color of the summer?  Or what image do you have for the color?

When I read my Dear friend Barbara's post and seeing lovely girls in blue dress at the wedding in summer time (the perfect color, don't you think). I wondered why "blue" has the meaning of "feeling depressed".  Well, maybe gray can be apposite color.  I checked about it and thought funny that this color has two opposite images.

Quote from this page      

http://en.wikipedia.org/wiki/Blue 

blue was related to rain, or storms, and in Greek mythology, the god Zeus would make rain when he was sad (crying), and a storm when he was angry.

The phrase "feeling blue" is linked also to a custom among many old deepwater sailing ships. If the ship lost the captain or any of the officers during its voyage, she would fly blue flags and have a blue band painted along her entire hull when returning to home port.

Conversely blue, a very popular colour^[7] can represent happiness and optimism^[8] as days with clearer, blue skies tend to be considered times where these emotions are more easily expressed. Many artistic contributions have been made referencing clear days with blue skies as part of the happiness or as a symbolism of the happiness the artist felt,

I know green has the image of  "young or not matured".  I wonder if there are more meaning hidden in colors in English. Anyways, summer heat DOES making me"FEELING BLUE" rather than "blue sky" image.

ps> I'm so grateful that my friends introduced me some other examples♪♪♪

"green with envy/ jealousy" or "green around the gills/ out of shape" 

"in the pink/ in good health"   "be tickled pink/ be amazed or pleased" 

"seeing red/ become very angry"  

"blue-blood/ someone from royalty or the aristocracy or an Old rich family" 

And last one is Ninny's explanation which I think I should put here.

If one is yellow or even green, one is really sick to the stomach. In the pink, one is feeling very happy. A healthy heart pumps red blood, but a sick heart makes the body turn blue, so I guess if we're emotionally healthy we're in the pink and if we're not emotionally healthy we're blue. The heart is synonymous with our emotions.