Final answer:
Nick's initial description of Gatsby is ambiguous because it is filtered through the eyes of a flawed narrator, making the story both personal and universal.
Step-by-step explanation:
The ambiguity in Nick's initial description of Gatsby stems from the narrative style of F. Scott Fitzgerald. While Gatsby is presented as great, his life is uniquely his own and should not be seen as representative of others during the 1920s. Fitzgerald utilizes Nick Carraway, who is a flawed narrator, to tell the story, which means we don't know all of Gatsby's secrets. This approach makes Gatsby's story both individual and universal, as the reader is drawn into the personal and mysterious aspects of his character. The narrative embodies themes that are significant for the post-World War I era, with colors like green, white, and grey symbolizing hope, false purity, and decay, respectively. This narrative style reflects the ambiguity of the era and adds depth to the characters' portrayals.