I would say the that the tone of Columbus' letters represents excitement and pure confidence. Part of this is manufactured by Columbus himself. He immediately sets out to write letters to officials in Spain to justify and cost of his current expedition and future voyages. He has to create a general mood or feeling of conquest and success because his ability to finance further support for his endeavors hangs in the balance of what he did on this one. Given the fact that the letters are written to high ranking Spanish monarchy officials, it makes sense that he would create a tone of excitement and the sense of wonder about his accomplishment. Many believed him. Columbus' letters and diaries were big selling literary products of the time period precisely because it embodied the wonder of exploration that was so intrinsic to the context in which Columbus lived and wrote. It is here where the tone has to be positive and overtly optimistic, never acknowledging failure of any kind or any possible misgivings. Such a tone is what helped create the narrative for so long about the Age of Exploration, and Columbus, in particular.