W.E.B. DuBois's famous "The problem of the Twentieth Century is the problem of the color line" is clearly suggested in Gaines's title, "The Sky is Gray." Illustrating the implications of the statement by DuBois is the heretical young black student who waits in the dentist's office. As voice of the "defiant, non-violent non-cooperation of the Civil Rights Movement" (enotes), this young man points to the grayness of the meaning of words such as freedom, liberty, white, colored--even God. Exemplifying his point, the young man tells a woman who asks him what color the grass is that it is black to prove his point that she believes it is green only because someone has told her it is green. "Words mean nothing. One means no more than the other."
The student's contention that words meaning nothing and only action counts affects James. After the confrontation of the young man with the preacher, James decides,
When I grow up I want be just like him. I want clothes like that and I want keep a book with me, too.
Like the student, James begins to think for himself; reaffirming his love for his mother--"I love my Mama, I love my Mama"--James indicates that he has already learned the lesson that one must define his life himself. Ernest Gaines's story is essentially existential.
I think the strongest insight revealed in this story is the cost of dignity and the resilience of the human spirit in the face of tremendous odds. James' mother Octavia is a proud and formidable woman who holds her head high in an environment offering her no equality and little comfort, and she teaches her son to do the same. Mired in poverty and forced to "sit in the back of the bus" both literally and metaphorically, Octavia does not complain. Although she is a single mother raising a family with few resources, she will not accept anything that even resembles charity, even refusing a small meal offered by a white woman in the city unless she and her son can do something in return. The price of maintaining her self-respect is great, however, and beyond what should be required of any individual in a society purported to be free and equal. Octavia raises her children to be hard in case they should ever have to carry on without her, demanding that James and his brother demonstrate the steeliness to kill two birds that they have caught, and James learns early that, denied access to medical treatment because of poverty and, indirectly, because of race, he must endure suffering - the problem of his toothache is never solved.
Many critics remark on the conflict of race in this story, and gear all conclusions surrounding the issues of prejudice and inequality. However, as your question is more broad than this, I will treat the answer more broadly. Putting race aside, what does James' experience in this story reveal about human existence?
This story is meant to be a Bildungsroman, a coming of age story. It details the events that this young boy will go through as he transforms from a child into a young man. The overwhelming lesson he is given resolves personal choice and personal dignity. His mentor in the maturing process is his mother, and his mother proves time and again that every action is a choice, and not a result being handed to you. She chooses how she will react to other people. She chooses not to receive charity. She chooses how and when to spend the little money that she has. No matter how gray the sky is, or how cold the weather is, she is not a victim, and she teaches James not to be one, either.