What is the subject of Arthur Rimbaud’s poem “Voyelles”?

In his sonnet "Voyelles" (Vowels), Arthur Rimbaud breaks from traditional subject matter by arbitrarily assigning a specific, unique color to each of the five vowels.1

The poem is often interpreted as an exploration of synesthesia—the association of different senses, in this case sight and sound—and may reflect the influence of Charles Baudelaire’s theories on poetry. Scholars have suggested various inspirations for the work, ranging from a child’s colored alphabet book to alchemy or intentional poetic obfuscation. Ultimately, the poem serves as an example of Rimbaud’s broader effort to achieve "the derangement of all the senses," a method he used to expand his consciousness and capture visions of the "unknown".12