Behind the curtain, in concealment; in secret. -- Curtain lecture, a querulous lecture given by a wife to her husband within the bed curtains, or in bed. Jerrold.

A curtain lecture is worth all the sermons in the world for teaching the virtues of patience and long- suffering.
W. Irving.

-- The curtain falls, the performance closes. -- The curtain rises, the performance begins. -- To draw the curtain, to close it over an object, or to remove it; hence: (a) To hide or to disclose an object. (b) To commence or close a performance. -- To drop the curtain, to end the tale, or close the performance.

So when the sun in bed
Curtained with cloudy red.
Milton.