Several key word searches through several e-text copies of The Great Gatsby have revealed that the only reference to the "green light" motif in Chapter 1 is most definitely found on page 21. It is at the end of this chapter when Nick sees Gatsby for the first time. Nick has just returned that evening from visiting Daisy and Tom Buchanan when, while sitting in his car parked under the shed, he sees whom he believes to be Mr. Gatsby come out of his mansion. Nick sees Gatsby "stretch out his arms toward the dark water in a curious way" (pg. 21). Nick looks out over the water and sees a "single green light," the same green light that is at the end of Daisy's dock (pg. 21). This is most definitely the only reference to a green light in the first chapter.
However, there is an indirect reference to the color green found on page 2. Nick refers to the fact that he has just returned as a soldier from World War I and wishes that all of humanity still adhered to the strict discipline that soldiers in uniform adhere to, as we see in his lines, "When I came back from the East last autumn I felt I wanted the world to be in uniform and at a sort of moral attention forever" (pg. 2). The reference to military uniforms is also a reference to or an allusion to the color green because a soldier's uniform is a deep "army" green. Since the color green refers to military uniforms in these lines, the color green is also symbolizing the fresh, pure, greenness of morality. The greenness of the uniforms acts paradoxically with respect to the green light on Daisy's dock as Daisy represents an absence of principles and morality.
Hopefully those comments help; if not, you may also want to consider that the page 2 reference on your assignment sheet is a typo and ask your instructor about it.