Perhaps the colors of the couches are meant to be significant, but it is hard to know definitively. However, considering the furnishings is a sound analytical move.
Because the room is one that Garcin, Estelle, and Inez are to share for an eternity in hell, one could reasonably assume that the furnishings are meant to be in some way punishing.
The description of the room being decorated in Second Empire style is significant. It is a highly ornamental style meant to suggest majesty and permanence, which is in itself ironic for the "style" of hell. Moreover, in the modernist period when this play was written, contemporary tastes had turned to more modern, streamlined styles, so to be stuck in an overly formal, uncomfortable, and fussy style would add to the misery of a more modern-minded inhabitant.
Garcin finds the bronze sculpture on the mantel ugly, and Estelle finds the couches hideous. Inez uses the word "livid" to describe the green of one of the sofas; it implies that the color is hard on the eyes.