In Langston Hughes' poem, "I, Too, Sing America," the author uses an extended metaphor.
eNotes.com provides the following definition:
An extended metaphor, also called a conceit, is a metaphor that continues into the sentences that follow. It is often developed at great length, occurring frequently in or throughout a work, and are especially effective in poems and fiction.
This extended metaphor is not very long. Figuratively, the poem seems to be saying that the speaker is like the black sheep of the family, though in this case, he is called the "darker brother." He is sent to the kitchen when company comes so that the family is not embarrassed by him.
I am the darker brother.
They send me to eat in the kitchen
When company comes...
But the speaker will use this time of separation for preparation—to grow stronger. In the second stanza, and the speaker refers to tomorrow, when he will sit at the table when company comes, and not be sent away.
I'll be at the table
When company comes.
The speaker says that at that time, no one would dare to tell him to eat in the kitchen.
The closing lines conclude the message of the poem with a sense of hope: people will see that he is really beautiful—nothing and no one to be embarrassed by—and they will be ashamed by their earlier behavior. He states that he also has the right to sing as an American.
The speaker is presenting a metaphor for racism. He starts out by stating that he is an American, but that he is treated like someone the "family" or country is ashamed of, segregated from the rest of society, eating in another room, or literally in a place where only whites are allowed. He will, however, bide his time where he has been sent, and grow stronger and work hard to obtain and enjoy the rights that all people should enjoy in the U.S. regardless of race or ethnicity.
In the second stanza, he refers to "tomorrow," which means some time in the future. The speaker says his time will come when he will be seen as an equal that no one will dare to dismiss or treat differently. The time of his repression will be over.
In conclusion, he believes that people will be able to see his worth, not by looking at the color of his skin, and they will be ashamed for the way they have treated him (referring to all black Americans). He ends the poem stating that he is also an American who can sing the song of freedom and equality.
This is my interpretation.