I've heard the use of "blue" word in substitution of "blues", and i was wondering if this has any sense. I was searching the web i couldn't find any reference to the use of "blue".
Is there any situation where the term is applied? "lets play a blue?", "do you like that blue standard?", something like that?

Feeling blue = getting the blues - they both mean feeling sad.

When it comes to music I don't really think you can substitute "blues" with "blue", but then again you can't give a definitive verdict when it comes to slang...
Guthrie Govan = Guitar Genius
Quote by Stud_Muffin
i thought blue note meant a note that wasnt in the key signature, like an accidental?

No its the flat fifth in a key.