Many scholars suggest that the color white symbolizes Ishmael's search for spiritual truth.
White is a color usually associated with innocence and purity, so it is unusual that the white whale should strike such fear in Ishmael and the crew. Throughout the novel, Ishmael describes many things, both good and evil, including religious practices, associated with the color white. He especially focuses on how unusual it is to see something fearsome that is white. He talks about polar bears being terrifying and the whiteness of a human corpse.
His struggle to understand how white things can be fearsome or threatening when white is usually associated with good mirrors his inability to understand how a god associated with good can allow evil.