You are right to be concerned about finding the themes in this novel! A Brighter Sun has a primary theme of change throughout the book. However, there are other themes that are not as obvious. Redemption is another theme, realized as Tiger becomes a man. The change occurs throughout, especially in Tiger's desire to rise above his class status.
Even though Tiger and his wife Urmilla are from the lower class, Tiger has experiences that create a desire within him for greater possibilities than can normally be achieved. How is this possible? Tiger is taught how to read, which opens an entirely new set of information and understanding.
When Tiger's farmland is taken by the American Military in order to build a highway, Tiger becomes a construction worker rather than remain a peasant farmer. Even though Tiger has many difficulties being a member of the lower class, he falls in love with his native country, Trinidad. He desires to rise above his situation in life, yet has great difficulty in understanding the class divisions and inability to navigate within them. He is told what is expected of him according to his low class status:
You gettam house which side Barataria, gettam land, cowwell, you go live dat side. Haveam plenty boy chile—girl chile no good, only bring trouble on yuh head. You live dat side, plantam garden, live good.
After becoming drunk with his American bosses, whom he invites over to dinner, he displays his angst towards the class system by beating his pregnant wife. Even in this event, class division remains as several doctors from the upper class refuse to treat Urmilla. He finally finds an American doctor who treats Urmilla; unfortunately, the baby is stillborn. After trying to redeem himself with an appropriate doctor and being unsuccessful, Tiger begins to build a better living hut for himself and Urmilla. There exists hope in their future through Tiger's acts of redemption.