Fitzgerald uses many symbolic devices to convey the thoughts and motifs 
of the 1920s. This symbolism is seen in the green light on Daisy's dock,
 the billboard on the side of the highway, the cars, the library in 
Gatsby's house, and Daisy's appearance.
From a distance, Gatsby sees a green light on Daisy's dock. This light 
represents the pursuit of the American Dream as well as a symbol of new 
wealth and life. His dream ends tragically, however, after being exposed
 to the corruption and violence that were a result of prohibition. His 
dream is simply an illusion. 
Plastered to a billboard, the eyes of Dr. T. J. Eckleburg tower above 
the side of the highway in the valley of the ashes. His large blue eyes 
are symbolic of God's watching over them, who has been reduced to an 
abandoned billboard. Corruption of spirit in the wasteland is also 
symbolized by the color blue, which represents the destruction of 
reality. 
Fitzgerald uses a gradual change in color to show the symbolism of the 
car used by Gatsby. At first, Gatsby's car is a cream color, but it soon
 evolves into a yellow instrument of death. Yellow symbolizes money and 
materialism that eventually leads to the destruction of the American 
Dream. 
Gatsby's library displays the materialism present in the 1920s. When 
Nick looks at the books on the wall, he notices that the edges of the 
books have not been cut yet and therefore have not been read. The 
library is a symbol of Gatsby's status, showing that he is able to 
afford and own a large collection of books. 
The color white is used by Fitzgerald to describe Daisy's 
superficiality. White is a symbol of purity and innocence, and Daisy 
first appears to be pure. Her actions soon explain, however, that her 
innocence is only a facade. To make herself appear "white," she drives a
 white car and even dresses in white. A similarity is seen in an 
ordinary egg. The outside shell is white, but the inside of the egg is 
yellow; these characteristics represent Daisy's sin.
also
As well as shedding light on Gatsby’s past, Chapter IV illuminates a 
matter of great personal meaning for Gatsby: the object of his hope, the
 green light toward which he reaches. Gatsby’s love for Daisy is the 
source of his romantic hopefulness and the meaning of his yearning for 
the green light in Chapter I. That light, so mysterious in the first 
chapter, becomes the symbol of Gatsby’s dream, his love for Daisy, and 
his attempt to make that love real. The green light is one of the most 
important symbols in The Great Gatsby. Like the eyes of Doctor T. J. 
Eckleburg, the green light can be interpreted in many ways, and 
Fitzgerald leaves the precise meaning of the symbol to the reader’s 
interpretation. Many critics have suggested that, in addition to 
representing Gatsby’s love for Daisy, the green light represents the 
American dream itself. Gatsby’s irresistible longing to achieve his 
dream, the connection of his dream to the pursuit of money and material 
success, the boundless optimism with which he goes about achieving his 
dream, and the sense of his having created a new identity in a new place
 all reflect the coarse combination of pioneer individualism and 
uninhibited materialism that Fitzgerald perceived as dominating 1920s 
American life.
one more..
The green light is of great significance in the novel, 
Great Gatsby. This symbol is depicted throughout the novel. It is first mentioned in the first chapter of the novel. At 
first, it was no more than a green light. When it is 
further examined in chapters four and five it becomes more
evident that this green light is not Daisy, but a symbol
representing Gatsby's dream of having Daisy. The fact that 
Daisy falls short of Gatsby's expectations is obvious. 
Knowing this, one can see that no matter how hard Gatsby 
tries to live his fantasy, he will never be able to achieve
it. Through close examination of the green light, one may
learn that the force that empowers Gatsby to follow his
lifelong aspiration is that of the "American Dream." 
 Nick realized what Gatsby did not. Right after he spoke of
Gatsby seeing the light on the dock, he said:
 
"...He did not know that it was already behind him,
somewhere back in that vast obscurity beyond the city,
where the dark fields of the republic rolled on under the
night."
 
Fitzgerald uses the green light as a symbol of hope, money,
and jealousy. Hope signifies the center of the dream, but jealousy and the lure of money pollute it. Gatsby is a
noble man whose vision is fouled by his dream because he
remains in a "wonder" at Daisy's presence throughout the
novel.
 The Green Light
Situated at the end of Daisy’s East Egg dock and barely visible from 
Gatsby’s West Egg lawn, the green light represents Gatsby’s hopes and 
dreams for the future. Gatsby associates it with Daisy, and in Chapter I
 he reaches toward it in the darkness as a guiding light to lead him to 
his goal. Because Gatsby’s quest for Daisy is broadly associated with 
the American dream, the green light also symbolizes that more 
generalized ideal. In Chapter IX, Nick compares the green light to how 
America, rising out of the ocean, must have looked to early settlers of 
the new nation.
The Valley of Ashes
First introduced in Chapter II, the valley of ashes between West Egg and
 New York City consists of a long stretch of desolate land created by 
the dumping of industrial ashes. It represents the moral and social 
decay that results from the uninhibited pursuit of wealth, as the rich 
indulge themselves with regard for nothing but their own pleasure. The 
valley of ashes also symbolizes the plight of the poor, like George 
Wilson, who live among the dirty ashes and lose their vitality as a 
result.
The Eyes of Doctor T. J. Eckleburg
The eyes of Doctor T. J. Eckleburg are a pair of fading, bespectacled 
eyes painted on an old advertising billboard over the valley of ashes. 
They may represent God staring down upon and judging American society as
 a moral wasteland, though the novel never makes this point explicitly. 
Instead, throughout the novel, Fitzgerald suggests that symbols only 
have meaning because characters instill them with meaning. The 
connection between the eyes of Doctor T. J. Eckleburg and God exists 
only in George Wilson’s grief-stricken mind. This lack of concrete 
significance contributes to the unsettling nature of the image. Thus, 
the eyes also come to represent the essential meaninglessness of the 
world and the arbitrariness of the mental process by which people invest
 objects with meaning. Nick explores these ideas in Chapter VIII, when 
he imagines Gatsby’s final thoughts as a depressed consideration of the 
emptiness of symbols and dreams.