One of the first things the casual reader might know about Walter Mosley is that he is a man of colors. The titles of his Easy Rollins mysteries each contain a color, from "Devil in a Blue Dress" to "A Little Yellow Dog," and one of his four novels outside that series is "Blue Light."

In "Walkin' the Dog," his second Socrates Fortlow book, Mosley is as colorful as ever. In just the second paragraph, Fortlow recalls his Aunt Bellandra's stories about "the black race in a white world under a blue god" and before 10 pages are out, 10 different hues have colored Mosley's prose, most of them more than once.

One of the next things the casual reader might know is that Walter Mosley is a man, and writer, of color. With the detective Rollins, he paints portraits of black life in Los Angeles at mid-century, and with Fortlow, his sketches move into the present.

Fortlow, nearly 60 but still enormously strong, spent half his life in an Indiana prison for murder and rape. But in the nine years he's been out, he has sought out a righteous path, taking on the rearing of an unguided teen who himself has killed, caring for sick friends and street people, and standing singly against a policeman's injustice, even when he is arrested, and then ousted from his job.

Mosley long ago proved that he is skilled at narrative and phrasing, and "Walkin' the Dog" reinforces that distinction, such as when he describes Charlene, whose strict Baptist upbringing has caused her to hate her beauty and look for men who'll mistreat her: She's "still in the streets, trading a slapper for a shouter, turning in good men for tramps."

But the meat of "Walkin' the Dog" is not in its stories, but in its doggedly philosophical inquiries, entirely befitting a main character whose name is Socrates. Primary targets are God and religion. Fortlow learned about the Lord as a child from his crazy Aunt Bellandra, who told him that God resides remotely at sea. Her "blue God" barely notices humankind, and has reserved an angel for black men who comes only when practically all has been lost.

That angel appears to present himself on the book's opening page, in the form of a thieving, drunken horn player named Hoagland Mars. Much later on, Fortlow finds Mars on the street, barely alive and deep in squalor, and carries him to an inn. Even after Fortlow has agreed to pay for Mars's lodging for the first three months and Mars is back on his feet, the trumpeter offers only the most tepid of gratitude, saying he would have found the haven anyway. (It is operated by Luvia Prine, whom he describes as "mean in a way that only some Christians seemed to master," another dig at organized religion.)

Mosley's questions are universal -- the caprices of God, the burdens of violence on the soul, the nature of guilt -- but Mosley focuses them in the black community. In the first Fortlow book, "Always Outnumbered, Always Outgunned," Mosley had Fortlow frequent a mom-and-pop bookstore, presumably in Watts, that was an oasis of black literature and thought, both on its shelves and in the informal discussions that thrived in its reading room. But the Capricorn was destroyed, and its mom and pop were taken with it, during the 1992 riots, undoubtedly Mosley's comment on how rageful violence does not discern in what it destroys.

The discussion-group device was so valuable to Mosley that he had to re-create it for "Walkin' the Dog"; this time its role-players gather at a neighborhood funeral parlor. In one scene in the penultimate chapter, they ponder whether black people have a right to be angry at whites, or if they "don't have no excuse for the misery down here an' everywhere else."

Fortlow, who raises the topic, explains that he's been noticing his anger, and noticing that it doesn't help. "I'm tired'a bein' mad, man. Tired. I see all these white people walkin' 'round and I'm pissed off just that they're there. And they don't care. . . . They thinkin' 'bout what they saw on TV last night . . . some joke they heard." One participant angrily questions the question. Another offers, "We got reasons. But reasons and rights ain't the same thing." Ultimately, they agree they can't settle the issue in one night.

Later, Fortlow almost gives in to his anger and strikes out at a rogue cop who has preyed on black people, but decides to attack in a different way, leading to the book's climax.

It can sometimes be difficult to climb the mountain of thought in "Walkin' the Dog," and it is obscure or confusing in small ways, but its meaning and style of expression make it a rewarding exercise. It is a public service as well: While Mosley is raising issues he thinks should be discussed in the black community, he's giving white people glimpses of black life we rarely could otherwise see.