What does blue sunglasses mean?

In The Famished Road, an unnamed white man asks Azaro's mother how to get out of Africa. She tells him a piece of traditional African wisdom through a riddle: "the only way to get out of Africa is to get Africa out of you." In return, the man gives her the blue sunglasses. The man wanders throughout the continent, until he finally understands the meaning of the riddle: to get out of Africa, he must learn how to be African. When he meets Azaro's mother again, he is a black Yoruba man:

They were shocked to see a mad white man in Africa . . . Then one day my head cleared. Five hundred years had gone past. The only way to get out of Africa was to become an African . . . I got a plane and arrived in England . . . Then before I turned seventy I had a heart attack and died . . . Time passed. I was born. I became a businessman. And I came to the market today to buy some eels and I saw you.

This tale contributes to the novel's element of magical realism. For Azaro's mother these events occur over a period of several weeks, while centuries pass in the man's perspective. Moreover, it plays into the theme of change and transformation as a result of cultural interactions. Both Azaro's mother and the man trade what they have from their respective cultures; Azaro's mother feels relief from using the sunglasses as a means of shielding her eyes and her advice allows the man to return home. The sunglasses story ties into the author's conception of African within the novel as an ongoing discussion of racial, geographical, and cultural solidarity.
The blue sunglasses can also be interpreted as an ironic metaphor for perspective: only when the man gives up his sunglasses and sees the true meaning of the riddle, is he able to find his way home. Ben Okri's novel, and this story-within-story in particular can be interpreted as a political allegory on colonialism. The white man has figuratively consumed Africa, then becomes what he has consumed. The 500 years that the man refers to can be interpreted as the centuries of colonialism the continent has been subjected to. As Avaro's mother shares the story, it then becomes one of colonialism told in the perspective of native Africans.