Getting a commission to do a mural for the posh Four Seasons Restaurant in Manhattan ought to be a feather in anyone's cap. Hell, the Park Avenue commission is the largest in the history of modern art. But in playwright John Logan's 2010 Tony Award winner, Red, this isn't Leroy Neiman that we’re talking about. It's abstract impressionist Mark Rothko, an artist of unassailable stature, so the notorious commission is both a dilemma and a daunting challenge. Centuries after the visual arts flourished under the wings of the Vatican and the Medici, modern art is already enshrined at the Whitney, MOMA, and the Chicago Institute — so as Rothko labors over his masterwork in 1958-59 down in the Bowery, he and his assistant Ken are ahead of the curve in pondering the question of whether he's "selling out." Not to mention the pressure of coping with a publicity culture. Robert Kahn, off a fine debut as the mad violinist in Opus, will be Rothko, and the ultra-versatile Jeremy DeCarlos is Ken.