Phrase indicating the approach of a somewhat loopy depression attack, as in The Nice Painter and his Wife - a sketch from the Fast Show in which a peaceful scene of watercolouring is invariably disturbed by the painter's aversion to a certain colour:

Him  Yes, I shall... I shall need to get the black out. 
Her  Johnny!
Him   Yes.  Black!  Black!  BLACK!  Like the clouds of DEATH that follow me into the Forest of DOOM!  And hide in the wardrobe of DARKNESS!  BLACK!
(He smudges black all over his painting) 
Him
 BLACK!  BLACK!
(now he does the same to her painting)
Him 
BLACK! 
(then he kicks the paint box over)
Him 
BLACK!  Listen!  Listen!  Do you HEAR?  The moon is weeping in a secret room!  They tap at my window, with tiny pools!
(slight pause)
Her 
I-I think we'd better be going home now, Johnny.