Blue--particularly medium-dark blue--is my favorite color. It is Oxford blue, the color of my university, and star athletes are awarded a "blue". (Rumor has it that "blues" are also awarded at the Other Place, but in the Fens the folk use that insipid light blue.) Blue is also one of the two colors of my local favorite, the University of California's main campus in Berkeley. It is the color of the St. Andrew's Cross, to be seen on the Scottish flag. Being of half Scottish heritage, I support Scotland in sporting events, but I am happy that dark blue is also found on the Stars and Stripes - and on the Union Jack also, for good measure. As a former Naval Officer, I like "Navy Blue".
In many respects, blue is a happy color. My father kept a pedigree Jersey herd, and our cow barn at my first home was decorated with a lot of blue First Place prize certificates. As a Bow Group left-of-center Tory in England, i was glad to wear a blue rosette on Election day. We enjoy blue skies, and prefer sailing in blue water. A trustworthy ally may be considered "true blue". In a hierarchical society, the aristocracy is alleged to have "blue blood". Ships are made to sail, so it is positive when the Blue Peter flag is flying, indicating the vessel's imminent departure. Bluebells and Texas Blue Bonnets are attractive flowers. The Blue Grotto and a blue lagoon are renowned for their beauty. Blueberries are delicious. A Blue Ribbon committee normally commands respect. A possibly glorious future is "beyond the blue horizon".
Then there is the other side of the coin: If you are unhappy, you have the "the blues". Melancholy music is described as having blue notes. In freezing weather, we can turn blue. If you're afraid, you may be in a blue funk. A blue baby will die if not treated promptly. A censor uses a blue pencil to delete unacceptable text. Obscene humor is "blue". Some folk curse a "blue streak" Most of us dislike the insect known as a "bluebottle". Spoilsports may be "bluenoses". Blue Sky laws help limit fraud. A "Blue Norther" in Texas brings unwanted cold weather.
Sometimes the word emphasizes rarity, as in the phrase "once in a blue moon". Another neutral usage is the "blue plate special", our version of the plat du jour.
Indeed, this is a very ambiguous color....