The use of striking, bold, 'primary colours' in the setting for this scene is highly significant. These colours symbolise the unalloyed, primitive nature of the poker players. They are all rough, hearty, uncultured, passionate men, with no pretensions to civilised behaviour (except Mitch, to a certain extent) and their game ends in sheer violence. The allusion to 'the raw colours of childhood's spectrum' also underlines this, childhood being a primal time before the notions of civilised behaviour take full hold.
Furthermore, Van Gogh is referenced as he is a painter who is famous for his use of vivid colour. The scene thus takes on wholly lurid overtones. The game's eruption into violence - Stanley hitting his wife and destroying the radio - foreshadows the even more violent climax of the play, when Stanley rapes Blanche.
In contrast to the vivid colours worn by the men, there are descriptions of the sisters wearing light, delicate colours, like Blanche's 'pink silk brassiere' and 'white skirt' and Stella's 'light blue satin kimono'. However, Blanche then slips into a 'dark red satin wrapper' which is more like the brilliant colours the men wear, and signifies her ability to compete with them. She puts on the radio which distracts the men and ends up enticing Mitch away altogether from the game.
We can also note that the radio is described as being 'small' and 'white'; it is a medium of art and culture (the music that Blanche puts on), which is quite different sort of entertainment to the rawness of the poker game. Similarly, Mitch's little silver cigarette case, which he shows Blanche, symbolises his softer side which he can indulge when alone with her and away from the other men. These colours, white and silver, contrast significantly with the vivid colours around the poker table.
Blanche is terribly upset at how the poker night ends, but the mild-mannered Stella takes it all in her stride.
..when men are drinking and playing poker, anything can happen. It's always a powder keg. (scene 4)
Stella, then, simply accepts the men's rough primitive nature and the inevitable consequences of this as being all part of the scheme of things.