What is the tone?

Tone is generally determined by several factors.  In
Langston Hughes's poem "Harlem," tone can best be determined by his use of imagery. 
This work has a simple structure: it is a series of images which draw a picture of the
answer to a question he asks but never answers:  "What happens to a dream deferred?" 
The images that follow are possible answers to that question and full of sensory details
which lead to a feeling of hopelessness. 

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Does it dry up
like a raisin in the
sun?

Here we have the visual
and tactile image of something once full and ripe which is now shriveled and dried
up--like a dream deferred.

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Or fester like a sore—
And
then run?

This image is one
of a partially crusted but mostly open sore which has not healed; instead, it oozes its
ugly fluids and never really heals--like a dream
deferred.

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Does it stink like rotten
meat?

The image here is one
of a life-giving substance which is now inedible and has the look and smell of
decay--like a dream deferred.

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Or crust and sugar over—

like a syrupy
sweet?

Here I think of
something like maple syrup left to dry up on a plate--hard and crusty and no longer
smooth and usable--like a dream deferred.

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Maybe it just sags
like a
heavy load.

This image is one
of pure weight, a burden which will not be lifted.  Visually, the word "sag" depicts an
utter hopelessness--like a dream
deferred.

Or does
it explode?

Finally, all the
senses are invoked in this image--sound and sight and touch and smell and even taste, as
the smoke and dust of an explosion fills the mouth.  There is nothing left; all is
lost--like a dream deferred.

This structure of rhetorical
questions replete with sensory images and details is designed to create a growing sense
of hopelessness, which it seems to me is both the tone and the theme of this
poem.