Blue, as in DEPRESSED.
The Big Bang Theory Season 4, Episode 22
It's Christmastime and
Jimmy Stewart's really DEPRESSED
The Big Bang Theory Season 7, Episode 11
...because I'm fun,
I'm not clinically DEPRESSED at all.
The Big Bang Theory Season 6, Episode 5
He's DEPRESSED because he's pathetic
and creepy and can't get girls.
The Big Bang Theory Season 2, Episode 12
...green is jealous
and blue is DEPRESSED.
The Big Bang Theory Season 4, Episode 22