Kimbell director Eric Lee giving a tour of the new Piano Pavilion. All photos by Jerome Weeks

• Jerome Weeks will interview architect Renzo Piano at the Will Rogers Memorial Center tonight at 7 p.m.

The word pavilion seems to have been originally and rather poetically mistranslated from the Old French word for butterfly: papillon. Instead, it was used in medieval English — and is still used — to designate a tent or canopy (think of a butterfly’s wings). But in architecture, it became a term for a “light, ornamental building or a pleasure-house, such as those common in parks or gardens,” according to the OED.

The museum as pleasure-house; there’s a thought. The Kimbell has insisted that the new Renzo Piano-designed addition to the museum be called a pavilion and not a wing or extension. Rightly so, because wings and extensions are physically connected to the main building, while the freestanding Piano Pavilion faces the original Louis Kahn building across the Kimbell’s lawn (also originally designed by Kahn and his mistress Harriet Pattison). They’re a ‘set.’ The Kimbell Museum is now more of a ‘two-building campus.’

But the subordinate nature of a pavilion gives some idea of the new building’s elegant but deferential response to Kahn’s masterpiece. In the ’60s, Piano worked briefly for Kahn, whom he’s called one of his ‘masters,’ and as one of the world’s leading designers of smart additions, upgrades and new wings (the Morgan Library in New York, the Art Institute of Chicago), he’s regularly spoken of the need for a ‘conversation’ between the old and new, respect and freedom — and not a wholesale re-do or slavish mimicry.

In which case, Piano’s part in this dialogue — at least when it comes to the new addition’s exterior — is a decidedly self-effacing one, holding its hat in its hand. For one thing, the basic concept of having the Pavilion direct visitors from the underground parking to the ‘right way to enter the Kahn makes it seem from the get-go like a servant to the older masterwork.  And on a slightly overcast day, the light grey color of the building’s cement walls almost makes the whole thing disappear, blending it into the sky. Burying the back half of the structure underground only amplifies this feeling. It’s as if the Piano Pavilion is retreating in the face of the superior Kahn structure.

Sheer size or bulk doesn’t make a building commanding, of course, and Piano is clearly inspired by what he’s praised as the ‘modesty’ of Kahn’s design — hence its low-slung proportions, its intimate-feeling rooms. But the quiet reserve of Piano’s design is not helped by the fact that the boxy building’s three-part face gives us a central glass entryway (reflecting the Kahn) flanked by two grey concrete walls, the size of long billboards. Piano is doing subtle things balancing concrete columns, wood beams and glass ceilings, but step back, and the Pavilion offers little of visual interest to compare with the Kahn. The Kahn may face us in a similar, three-part fashion, but his entryway has a small grove of holly trees and his walls are made of travertine, which gives them a subtle, earthy-marble texture. They have classic, arched roofs while simultaneously seeming to float on low fountain pools. All of this is peaceful and delicately detailed, like some open-air Mediterranean courtyard.

In contrast, Piano’s walls are unadorned and blank, there are no refreshing pools. And the overall boxy shape and flat-roofed layout (with solar treatments) are what Piano has been playing with since his museum-design breakthrough with the Menil in 1987. But his earlier treatments (the Nasher, the Foundation Beyeler, the Cy Twombly) were handled with more verve and distinction.

It must be said, though, this external lack of presence is the weakest part of Piano’s design. Inside, that same, silky grey concrete does absolute wonders in the galleries. With the Kimbell, the Modern and now the Piano Pavilion, Fort Worth has a considerable investment in fine treatments of concrete — these are the most polished, the most refined walls yet. The rooms are caressed by the creamy sunlight pouring down from Piano’s skylights, striped by huge, pale wood beams that run the length of the building. Piano has retained the scale of the Kahn galleries — we’re not in cathedrals or blinding-white-cubes of modernism but in intimate, welcoming rooms.

There are other, new facilities the addition brings to the Kimbell — education rooms, for instance, and a small but smart-looking auditorium. But despite the journalist’s need to make snap judgments based on first impressions, the auditorium’s effectiveness can’t really be judged until we see/hear something in it. And I wasn’t able to visit the parking garage, to see how the new rising-up-facing-the-Kahn-entrance plan works in practice. In any event, the Piano addition will succeed or fail by what happens in the galleries.

So make no mistake: The chance to see a significant portion of the Kimbell’s permanent collection re-hung in these new galleries is not to be missed. It’s a lesson in the magical transformations that ambient colors and new curatorial displays can do for art. Pieces that a viewer overlooked suddenly step forward and assert themselves. The warm, yellowish tone in the Kahn could dim terracotta sculptures or gold paint until it seemed to fade into the walls. Here, the grey provides just enough rich, lovely contrast to make these same works pop. And old familiar friends are given new life. This viewer fell in love all over again with the delicate clay bust of Isabella d’Este — the Renaissance masterwork purportedly by Gian Cristoforo Romano that was retrieved from a Nazi salt mine.

Just by bringing together on a single wall the four, cloud-swirling, Roman-god allegories by Francois Boucher — part of a series by the French rococo painter — this new exhibition makes a case for them as epic works. They have never looked so sumptuous or so distinguished. And the pavilion’s darkened rear gallery turns just about everything in the Kimbell’s Asian art collection into a striking set piece, a glowing, individual icon.

Overall, the Piano Pavilion’s airy color scheme is augmented by handsome, white-oak floors and it’s adjusted by photovoltaic louvers in the roof and window shades everywhere. There’s also a meticulousness to the interior, Piano’s characteristic sense of polish. Whatever the outside’s low-profile humility, the interior is invigorating, sleek and quietly proud. It will be well worth visiting to linger at different times of the day, different seasons, watching the light change these works.

One of the pleasures of this pleasure-house.