During her opening song Friday night at Buffalo State College’s Rockwell Hall, Judy Collins compared friendship to a rainbow.

On paper, it’s a Hallmark greeting at best, an example of the kind of loopy folksinger treacle that inspired the Christopher Guest film “A Mighty Wind.” But this was coming from Collins, arguably the pre-eminent folk interpreter of the 1960s and ’70s, with a voice so pure it could lift the songs of Dylan and Cohen from their cocoons of pretension and set them free as butterflies.

My apologies for the ninth-grade poetry. It’s just that seeing Collins puts one in a marvelously optimistic frame of mind. She may be 73, but that voice is trapped in amber, and when coupled with her acoustic strumming and some accompanying piano, the sentiment of that opening tune, “Song For Judith (Open The Door),” felt like raw truth.

“Yeah, friendship is like a rainbow,” I thought, and for the rest of the night, Collins had me (and I’d imagine a large percentage of the packed house) slack-jawed and hypnotized.

Over the course of two sets – the first with the guitar and piano setup I’ve described, and the second featuring Collins alone on the ivories – we were treated to many of the songs that made her famous, including a few that helped to launch the careers of their writers as well.

“Both Sides Now” came early, the clouds that Joni Mitchell so famously pondered now an accurate description of the striking white nimbus atop Collins’ head. A stunning performance of “Sons Of” closed out the first set, with its Jacques Brel lyric describing us audience members quite accurately – “children were lost in lullaby.”

Set two was a more solemn affair, centered on the gut-wrenching beauty of “In the Twilight,” a song off Collins’ 2011 album “Bohemian” about the passing of her mother. Ambitious, serpentine passages supported lyrics stuffed with floral imagery, showing that the artist’s writing skills remain nearly as sharp as her singing.

“Albatross” was probably the highlight of the entire show for me, the piano chords a rolling countryside shifting from shadow to light, Collins’ voice the warm spring sky above it all.

Given the way everything started, it was only fitting that Collins closed the show proper with her take on “Somewhere Over the Rainbow.” To me, the original is neck and neck with “What A Wonderful World” in the race for the title of Most Depressing Song of All Time, but like I said, Collins already had us believing in this kind of thing. In her hands, the song made me feel like I really could fly with the bluebirds, that the black and white world is the lie.

As powerful as this all was, during the final tunes we were reminded that Collins was a human, and not some mythical sorceress. Starting with “Albatross,” she began to blank on some lyrics, only missing a beat before continuing. And when getting up from the piano to deliver “Rainbow,” she knocked a pile of sheet music onto the floor.

For sure, these moments temporarily broke the spell, which only accentuated the fact that we were indeed under one.