In principle it means "blue" (color), it comes from the medieval form blæwen and has similarity with many languages, which makes it difficult to trace whether it came to English from the Franco blau, from the Germanic blewaz, from the Latin blavus, . . . But the most notable thing about 'blue' is its informal meanings. Some are understandable, such as "cyanotic" (for the color of the skin) or for the bluish-gray fur of some animals (a proto-Indo-European antecedent named light hair or gray gray), but the "pale flame", because it is not red or orange, already begins to be curious; political colors can be a choice (p. and. British Conservatives who identify with the blue), although associating it with "obscenity and prostitution" needs a good excuse, and "sadness and depression", too (although in this case we can return to its common origin with the "gray", which is a sad color). As a fact about the latter, the plural blues is a musical genre. . . sad and profound.