Fugard's tone is light and happy at first. The "boys" are singing and dancing, and Hally joins in the fun. There's joking and happy reminiscing by everyone. This is a real escape for Willie and Sam from the pain of their everyday lives, and they talk about it with pleasure and excitement. Hally gets caught up in the happy mood until the phone calls from his mom bring him crashing back down to earth.
Gradually, things darken, and the play becomes tough stuff to read and see. You get increasing racial violence, hatred, abuse spewing left and right, almost all of it spoken. Hally curses constantly, and words are used as weapons. When Hally tells Sam to call him "Master Harold," Sam answers: "(Quietly and very carefully) If you make me say it once, I'll never call you anything else again" (1688-1689). Everything the characters say is measured and meaningful, and the meaning's often painful.
The lightness we saw early in the play makes these bitter moments even more heartbreaking to read.