"The blues" is a circuitous derivation from the English phrase "to be blown", i.e., to be knocked back, to the Southern US term "to be blewn" (phonetic) and therefore to have the "blues". Since 'the blues' originated in the Deep South evolving from negro slave songs then this expression makes sense? Hope it helps.

as a music form featuring flatted thirds and sevenths, possibly c.1895 (though officially 1912, in W.C. Handy's "Memphis Blues"); meaning "depression, low spirits" goes back to 1741, from adj. blue "low-spirited," c.1385. http://www.etymonline.com/index.php?term=blues The adjective blue has been associated with despondency and sadness since the 16th century. The noun the blues has been with us since 1741, when David Garrick penned the following in a letter: I am far from being quite well, tho not troubled wth ye Blews as I have been. The blues is a shortening of blue devils, demons popularly thought to cause depression and sadness. Blue devils have been around since 1616, from Times’ Whistle: Alston, whose life hath been accounted evill, And therfore calde by many the blew devill. The name of the musical style has been around since 1912, taking its name from the mournful and haunting nature of the lyrics. Some sources say the style takes its name from the blue notes that it uses, blue notes being a minor interval in place of a major, an off-pitch note. But the opposite is true. Blue notes get their name from the blues, not the other way around. Blue note is attested to in 1919. (Source: Oxford English Dictionary, 2nd Edition) http://www.wordorigins.org/index.php/site/comments/blue_blues/ Etymology: blue devils Date: 1741 low spirits : melancholy <suffering a case of the blues> http://www.merriam-webster.com/cgi-bin/dictionary?book=Dictionary&va=blues Alternative Names: Blues; Discouragement; Gloom; Mood changes; Sadness; Melancholy Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for short periods. True clinical depression is a mood disorder in which feelings of sadness, loss, anger, or frustration interfere with everyday life for an extended period of time. http://www.nlm.nih.gov/medlineplus/ency/article/003213.htm Colour psychology: Blue can also create feelings of sadness or aloofness. Blue is one of the most popular colors, but it is one of the least appetizing. Some weight loss plans even recommend eating your food off of a blue plate. Blue rarely occurs naturally in food aside from blueberries and some plums. Also, humans are geared to avoid foods that are poisonous and blue coloring in food is often a sign of spoilage or poison. Blue can also lower the pulse rate and body temperature. Consider how blue is used in language: blue moon, blue Monday, blue blood, the blues, and blue ribbon. http://psychology.about.com/od/sensationandperception/a/color_blue.htm Dislike Blues * If you dislike blue you may feel as though someone has been disloyal to you and let you down * You may also feel as though you have suffered a personal loss or failed a relationship * You may dislike speaking about yourself and communicating truly how you are feeling Unconstructive Traits * Anxious, suspicious, worriers, paranoid * Become defensive if they feel threatened * Needs to always prove that they can stand on their own – rarely ask for help * Own a great deal of self doubt – question everything! * Always needs to be prepared. Doesn't like to be caught off guard * Perfectionist * Preaches * Blames others for their problems * Difficult to open up in a relationship http://www.heavenlyideas.com/color-therapy/Psychology/blue.html Characteristics: Blue people are emotional and stay within themselves. They tend to not trust others as they carefully watch them. Pale blue is the color of devotion and reflects one who prefers things to be in order. As blue becomes darker, it becomes moody and depressed, hence the term, 'the blues'. Lovers of royal blue can be on either a large high or in a deep pit of emotion. Navy blue is favored by those who are very emotional but wish to conceal it. They tend to indulge themselves in their emotions and can, in extreme cases, become obsessed. Being feelers, they cry when they are happy or sad and as a result leave themselves wide open to others. They can easily guage the mood of any person they are around regardless of their state of mind. Blue personalities can't explain the range of their emotions, as they are products of their environment. Looking for sympathy in others, blue people can be miserable to be with when they expect you to be down with them. Codependently, they need you to feel as they do. Too much blue around will create depression so it needs other colors to balance it. http://www.bharatmatrimony.com/astrology/color.shtml