She has cultivated the intertidal zone demarcating representation and abstraction, creating composites in which each strategy maintains its character while allowing the other to assert itself.

In her most recent paintings, Osborne has traveled all the way to the abstract end of this continuum.

Collectively, her paintings have been introspective, demonstrative, evocative, mysterious, symbolic and poetic, sometimes several of these at once. Yet she has consistently displayed two defining attributes.

The first is her devotion to vibrant, sometimes unnatural color to generate energy, light and structure. Paradoxically, her color doesn't generate high heat; it's often cool, almost dispassionate.

Nine years ago, reviewing a show of her work at Locks Gallery, I described this commitment to saturated color as Dionysian. I observed that it was exquisitely balanced by an Apollonian sense of order and placement. The results are pictures that sing their hearts out, but always follow the score unerringly. Every shape is meticulously in its proper place, every brushstroke calculated for maximum effect. Impulse is banished: The paintings are constructed like Swiss watches designed by Matisse.

The Matisse allusion isn't hyperbole or flattery, it's evident the moment one walks into the Osborne retrospective in the academy's Hamilton building. As with Matisse, especially in his pre-Nice paintings, color for Osborne is more than sensation, it also creates structure.

This becomes strikingly evident in the 1970s, when she began to make elemental landscapes and seascapes such as Delos and Southwind.

However, we also find structural color earlier, in Portrait of James Havard (Red Interior) and Peale House (West View). A room suffused with chromatic intensity of this magnitude almost makes one's eyes water. So if you aren't familiar with Osborne's art, brace yourself and bring sunglasses.

The academy retrospective of about 50 paintings made over the last 40 years was organized by academy curator Robert Cozzolino. It celebrates the career to date of one of Philadelphia's most respected painters, a teacher at the academy since 1963.

A Philadelphia native, the 73-year-old Osborne studied at the academy from 1954 to 1958. Her teachers included the equally distinguished Philadelphia painters Jimmy C. Lueders, Ben Kamihira, Francis Speight, Walter Stuempfig, and Franklin Watkins.

I thought I detected a residual echo of Lueders' precise still-life style in Still Life With Amish Quilt and in Osborne's treatment of the still-life foreground of an ambitious, intense self-portrait titled The Studio.

California painter Richard Diebenkorn was another early influence that reveals itself in paintings such as Black Doorway and Renae. Diebenkorn translated interiors and landscapes into blocks and bars of contrasting colors in a way that whispers "architecture." Osborne's paintings often do likewise, - see, for instance, Studio Westward View and the interior called Color Field.

A third hallmark of Osborne's approach to painting emerges in this exhibition - she combines abstraction and realism naturally, effortlessly, and logically. This is perhaps most evident in the boldly brushed, reductive landscapes and seascapes painted early in this decade, pictures such as Blaze III, Oracle I, and Slea Head.

These are all motifs from nature, and Osborne hasn't obscured that fact. However, by reducing scenes to interlocking planes of Fauve-hot, expressionist hues, she imparts to nature a jazzier alternative personality.

"Fauve-hot" characterizes the saturated intensity of her pigments; it doesn't imply that she also adopts the expressionist feverishness of that early modern movement. She's closer to Matisse, who could be coolly analytical and exuberantly colorful at the same time, and without seeming to contradict himself.

This dichotomy is even more apparent in Osborne's female nudes, which are as objectified and desexualized as Tom Wesselman's Pop interpretations of this classic genre.

Curator Cozzolino has installed the show thematically, and roughly chronologically, so one can follow Osborne's evolution from a nominal realist - again, the elaborate self-portrait called The Studio is instructive - to a painter for whom abstraction plays an increasingly important role.

As the paintings become more abstracted, her palette becomes correspondingly more electric, reaching a climactic intensity in the landscapes and seascapes from the mid-1990s into this decade.

This progression seems entirely natural; there aren't any abrupt stylistic or conceptual transitions. Consequently, by the time the viewer reaches the end of the hanging, denoted by the ethereal White Pond, the hallucinogenic Payne's Grey, and the three Rothko-like Lux paintings, the sense of an adventurous journey is manifest.

Note, though, that the three Lux abstractions, horizontal bands of contrasting colors, preserve a landscape structure with distinct horizon lines.

One other recent painting, Homage to EA, is worth noting. It's a geometric checkerboard inside a solid-color border that honors the late Edna Andrade, a friend and mentor who died in 2008.

This image might seem anomalous until one recalls earlier works like Interior With Quilt and Tulips With Red in which strong patterning is a major component. Another link to Matisse, perhaps.

Osborne's art is subliminally autobiographical and meditative, particularly about the art-making life and the studio environment that makes it possible. For instance, several paintings, particularly Artist and Bridge, include partial views out her Old City studio window of the Benjamin Franklin Bridge, which was designed by Philadelphia architect Paul Cret (1876-1945), her biological father.

Such interior monologues occur in many of Osborne's paintings, but they don't impede one's enjoyment of her shimmering formalist harmonies and her solid sense of compositional design. One marvels at the pleasing balance between pictorial intelligence and disciplined sensuality. It will be interesting to see what the next chapters of her already distinguished career will produce.

Art: The Color of Light

"Elizabeth Osborne: The Color of Light" continues in the Hamilton building of the Pennsylvania Academy of the Fine Arts, Broad and Cherry Streets, through Sept. 20. Hours are 10 a.m. to 5 p.m. Tuesdays through Saturdays and 11 to 5 Sundays. Admission to special exhibitions (includes permanent collection) is $15 general, $12 for seniors and students with ID, and $8 for visitors 5 through 18. Information: 215-972-7600 or www.pafa.org.