It was a celebratory homecoming when Animal Collective played at Merriweather Post Pavilion on Saturday night. (All photos by Kyle Gustafson/FTWP)

If tie-dye symbolized some expanded, psychedelic boomer consciousness, face paint represents 21st-century digital-age confusion. It’s both a day-glo war paint against normalcy and a nostalgia trip to the innocence of childhood — rebellion and regression, two threads inextricably intertwined in Animal Collective’s music.

When asked about the dollops of red and green and purple covering his body, a shirtless Eric Sponaugle of Olney says, “I just knew I wanted to do this with my life.”

Most tailgaters are less colorful, nursing cans of light beer, tossing bocce balls or listening to Tom Petty. One car’s license plate reads “STRWBJM,” a tribute to Animal Collective’s 2007 album “Strawberry Jam.” Other plates are from faraway states — dinged-up Mazdas and Hyundais driven by fans who drove hours to see the group finally play the stage mythologized by an album that was named 2009’s best by Spin, Pitchfork and the Village Voice’s Pazz & Jop critics’ poll.

Merriweather is where the members of Animal Collective, who grew up outside of Baltimore, saw some of their first outdoor concerts.

“I think they’re as excited to play at this venue as we are to see them at this venue,” says Daniel Habecker, here with a tribe from central Pennsylvania. His friend, Genesis Bordner, is twirling a hula hoop as “Brother Sport” — the closing tune on “Merriweather” — pumps from the trunk of their sedan. Nobody expects to hear this song tonight: The band’s defiance of expectations is what’s earned it so much loyalty.

“They really don’t care what the fans like,” Dylan Gallic says of the group. “They just want to do what excites them, and the fans understand that.”

Fans also know to give them space when they bound up into the stands hours before their set to greet family and friends. Dave Portner, better known as Avey Tare, runs up to row L where family members cover him in kisses. Josh Dibb, who performs as Deakin, delivers a hug to Lexie Mountain, the way-out folk singer from Baltimore. Four nearby teens remain fixed in their seats, trying to control their excitement like bobbleheads during an earthquake.

Up near the lawn, the body-painted Sponaugle is ready for the festivities to begin. Clutching a bamboo pole topped with a blue reflector and a feathery boa, he offers a prayer.

“Everyone, put your hand on the staff,” he says to a small congregation of buds and strangers. “Oh, great and powerful sun, grant me but a fraction of your guiding light so that I may see clearly.”

The sky darkens into a bruise and Seth Hurwitz is up there, too. The chairman of I.M.P., the promoter that programs Merriweather, says he remembers the day Animal Collective phoned him for permission to name its album “Merriweather Post Pavilion.”

“Of course, my Google [alerts] went nuts for a year, but it’s a great honor,” Hurwitz says. “This place has kind of a magic vibe to it. . . . The fact that these guys appreciate what Merriweather is and consider it the Wrigley Field of amphitheaters, I just think it’s great.”

Hurwitz tried to lure Animal Collective here shortly after the album dropped but says the group was in no rush. “That’s why they are who they are,” he says with a shrug.

When Animal Collective finally takes the stage, the lighting is dark blue and the stage is decorated with crystalline stalagmites, vines of lights and a giant, rainbow-tiled skull, like something out of “Goonies” or “Pee-Wee’s Playhouse.”

For 90 minutes, the foursome play almost all new, unfamiliar, untitled material. There are weird waltzes and doo-wop tunes and klezmer-ish romps, all made slippery and mysterious with improvisation.

As ever, who knows how it’s made. You can see Brian Weitz, a.ka. Geologist, pushing sampler buttons. You can see Noah Lennox, a.k.a. Panda Bear, pounding on a drum kit. But the music still seems to come from somewhere else. Lennox and Portner’s voices are swaddled in so many effects, it’s as if you can hear their words before you see their lips move. Fans’ faces on the Jumbotron are squinty and contemplative, their tender teenage brain tissue being gently re­arranged.

When the band actually plunges into “Brother Sport,” a song that everyone knows, the concrete floor of the general admission area turns into a moonbounce. Up on the lawn, fans sway like sea anemones while bros on the perim­eter grind up against phantom dance partners.

Two other “Merriweather” songs make it into the set — “Summertime Clothes” and “Taste” — but they’re torqued into new shapes, new textures. The new stuff is almost entirely sung by Portner, who thanks the audience — the venue was nearly two-thirds full — with an awed grin.

“It’s sweet to be here,” he says.

After one encore, the spell is broken by harsh fluorescent house lights. “Go home,” they seem to say, “and wash that stuff off your face.”