"Oh, I am a lonely painter, and I live in a box of paints," sings Joni Mitchell somewhere near the end of her third and most recent LP, Blue (Reprise MS 2038). But the description applies not only to the singer, but the songs.

Because her music has been introspective much of the time, and because her approach is highly personal all of the time, the 10 songs on Blue will undoubtedly be used by fans as a chart to find what course her mind has set. But even for the most obvious of singers, this can be hazardous; and trying to sort out Joni's elliptical songs can be confusing at the best of times.

This is not to say there's anything particularly obtuse about this LP. If anything, it's her best to date. The melodies are less operatic and diffuse, the accompaniment more varied, and her voice has a richer, less keening sound. Every song seems focused, and concisely conceived.

As with the songs she first tentatively tried out in the Riverboat (Yorkville entertainment house in Toronto) years before she moved to California's Laurel Canyon, those in Blue rely on visual imagery. She still paints in her spare time. In "All I Want," there are roads she travels down; in "Little Green," her images of crocuses and Northern lights go back to her Saskatchewan youth; and there's always some pretty men to help her when "them lonesome blues collide."

Her music registers easily in visual terms. While many of her images have remained constant, what she painted on her first two LPs in light colors now appears in darker tones. Their airiness has been replaced by something more substantial.

All of which make it easier for me to understand her work. At the Riverboat, when she was just starting to sing and I was just starting to write, we would argue about each song. To me, they seemed too impressionistic, too flighty ... too feminine. To her, they were "only what I see and feel - my experiences."

"Since I moved to California," she said some time later, "I know my life has changed. How it has changed my music? I guess it's too early to tell..."

That was about a year ago. But this LP gives clues to what's happened in the interim. She's begun to rely more on other musicians for accompaniment - in this case, Steve Stills, on guitar and bass, James Taylor on guitar and Sneaky Pete on steel guitar and Russ Kunkel on drums.