It is of course possible for any work of literature to have two tones or more, depending on its length and content. I think it is fair to say that, thinking about this excellent poem, that there are two tones that we can pick out. The defiance and arrogance of the speaker at the beginning of the poem is characterised by such lines as:
We real cool. We
The speaker obviously feels proud of the way he has left school and is engaged in various activities like "singing sin" and "lurking late" and this is an impression that is reinforced by the alliteration used throughout the poem. However, the very last line, with the way that the enjambment emphasises the word "die," adds a sad, sombre tone as the speaker realises the results of the kind of "cool" lifestyle he has chosen.