It is commonly accepted that in Elizabethan theatres black curtains indicated the playing of tragedies. One line in the anonymous play A Warning for Fair Women famously proclaims:
The stage is hung with black: and I perceive
The auditors prepared for tragedy.
But as Mariko Ichikawa pointed out in a recent article in Theatre Notebook, Elizabethan theatres possessed other curtains as well, sometimes with elaborate pictures on them. An inventory of the Lord Admiral's Men done in 1598 listed "a cloth of Sun & Moon" as well as a "Tasso picture" among the company's possessions. Since Torquato Tasso had introduced pastoral themes to the Italian stage with his 1573 play Aminta, this latter curtain probably depicted a scene of the countryside.
Thomas Kyd's The Spanish Tragedy has the hero Hieronimo hang up a curtain for a play-within-the-play at the end of the piece. This curtain, presumably black since Hieronimo is introducing a tragedy, might have replaced a curtain of a different sort that had been hanging earlier. Ichikawa argues convincingly that non-black curtains could have been hanging in the middle of tragedies, with the black curtains only prominent at the beginning and ending of plays. For tragicomedies, companies might have avoided black curtains at the beginning in order to keep the audience in suspense about the play's finale.
And other colors were certainly available. A lawsuit in the 1530s over the possessions used by a theatrical company listed two curtains of green and yellow. Though the Elizabethan stage could be hung with black, it could be hung in a variety of other hues as well.