In "The Color of Water", what does the imaginary boy in the mirror represent in childhood and adulthood?

In
childhood, the boy represents everything that James cannot be or have.

I created an imaginary world for myself. I believed my true self
was a boy who lived in the mirror. Id lock myself in the bathroom and spend long hours playing
with him. . . . I had an ache inside, a longing, but I didnt know where it came from or why I
had it. The boy in the mirror, he didnt seem to have an ache.

Thus James can take out all his anger & frustration on the boy in the mirror, who
will listen without ever judging him. On the one hand, James needs the boy to reflect what he
could have, but at the same time, he hates the boy because "he didn't have a white mother,
he never went hungry, he didn't have to share his bed."

As an adult,
James looks back on his imaginary friend as a symbol of what he has overcome. He had triumphed
over the fristrations and injustices the imaginary boy represented.