Conversation so far:
What was Mercury Theatre?
in 1937, Welles and Houseman founded their own repertory company, which they called the Mercury Theatre.
What did the company do?
Welles was executive producer.
What role did Houseman play?
CANNOTANSWER.
Did they write productions?
Caesar, Welles's modern-dress adaptation of Shakespeare's tragedy Julius Caesar.
How were their shows received?
Joseph Cotten later described as "so vigorous, so contemporary that it set Broadway on its ear..
Did they receive any other great reviews?
"I think he was the greatest directorial talent we've ever had in the [American] theater," Lloyd said.
Did he receive any awards?
Such was the success of the Mercury Theatre that Welles appeared on the cover of Time magazine.
What year did he appear?
the issue dated May 9, 1938--three days after his 23rd birthday.
What else did you find interesting about this time?
The set was completely open with no curtain, and the brick stage wall was painted dark red.
Scene changes were achieved by lighting alone.

Question: Why was this done?
Self-contained rewrite: Why was the set the completely open with no curtain and the brick stage wall was painted dark red?