BOOK REVIEW / FICTION : Scenes--and Skeletons--of a Troubled Southern Family : SIGHTS UNSEEN <i> By Kaye Gibbons</i> ; Putnam; $19.95, 209 pages

If Southern novelists were painters, most would work in oils and lay them on the canvas darkly and thickly: brilliant hues, violent chiaroscuro. Kaye Gibbons, in contrast, is a watercolorist, deepening her meanings gradually by strokes of a fine, pale wash.

Take the central scene of this short novel. In 1967, when the narrator, Hattie Barnes, is 12, her mother, Maggie, drives into Rocky Mount, N.C., and hits another woman with her Oldsmobile. The victim, she explains, wore a “red swing coat� just like her own and thus was trying to steal her soul. “If somebody had to be arrested,� she adds, “then what about locking up that bitch who was in there sniveling about her bruised, fat hips that could stand a clip off either side anyway?�

The first time Gibbons gives us this scene, it’s to illustrate the extremes of Maggie’s manic-depressive illness and the toll it has taken on Hattie, her brother, Freddy, and their long-suffering father. They have all had to adjust daily to her ups, downs and brief interludes of normality; she is the most important person in their lives, but they have no real presence in hers. Now, finally, the “sights unseen� except in the family circle have become a public scandal.

When the story doubles back to the car accident, however, we learn more. Maggie is shielded from prosecution by her widowed father-in-law, a landowner who has always indulged her whims. For the first time, his kindness toward her and his bullying of other people fit together; he has taken advantage of her illness to maintain a relationship incestuous enough in spirit so that when he starts “keeping company� with someone his own age, the woman treats Maggie as a rival.

Toward the end of the novel, we return to the scene a third time and see it as the prelude to Maggie’s healing. The scandal forces the family to abandon the reticences and evasions that have enabled her to get by as “the Barnes woman with all the problems.� She needs whatever the best hospitals can do for her, including electroshock treatment and medication.

This means, for everyone, entering the 20th Century. They have lived, as Hattie notes, in the spirit of the mid-19th, when “our farm would have been called a plantation; the house, the Big House; the tenant farmers, slaves; and my mother, a classic nervous matriarch who suffered spells.�

The caring and equable stranger who comes home in Maggie’s body comes none too soon for Hattie. “A girl cannot go along motherless without life’s noticing, taking a compensatory tuck here and there in the heart and the mind. . . . Had I not pitied my mother, I would have stopped waiting for her. . . . But we caught each other just in time.�

The narrative is a balance of Hattie’s childhood confusion, her and Freddy’s adult perceptions as doctors, the reminiscences of others and some inspired intuition about what the manic-depressive state feels like to the sufferer. “Sights Unseen� is a lucid family portrait, scrupulously fair to all the characters. Its tone is affectionate but unsentimental, cool and comic.

Skeletons do rattle in Gibbons’ closets, but quietly. The condition of African Americans, for example, is implied rather than stated. In young Hattie’s eyes, Pearl, the Barneses’ cook and housekeeper, is the devoted family retainer of legend. We are left to deduce for ourselves why a woman of such intelligence and ability has to cater to a mental patient in order to command a decent salary and a car and secure maid’s work for a teen-age niece whose own family can no longer afford to feed her.

The happy ending of “Sights Unseen� is tipped off at the beginning and arrives without twist or relapse, as if this novel really is what it pretends to be: a memoir enlivened by the techniques of fiction. This is trompe l’oeil --an imitation of life so faithful that it conceals much of its own art.