Meaning

adjective of the color intermediate between green and violet; having a color similar to that of a clear unclouded sky; - Helen Hunt Jackson

adjective used to signify the Union forces in the American Civil War (who wore blue uniforms)

adjective filled with melancholy and despondency

originFrom blue + -er (“Oxford -er”). Used at Harrow School in London, United Kingdom.

Etymology from Wiktionary, CC BY-SA 3.0