I'm terrible at telling the Three Dog Night singers (Chuck Negron, Danny Hutton & Cory Wells) apart when I don't see them, this vid is always helpful, because they all take turns verse for verse ...
I tend to envisage all their songs with Chuck Negron (Mr Mustache) singing lead, probably because I deemed him the most handsome and coolest looking as a teen. But really they shared all their many hits pretty equally as regards who sang lead:
Lead vocal credits:
"An Old Fashioned Love Song" – Negron
"Black and White" – Hutton
"Celebrate" – Hutton (Verse 1), Negron (Verse 2), Wells (Verse 3), who sings melody through the end refrain
"Easy to Be Hard" – Negron
"Eli's Coming" – Wells
"Joy to the World" – Negron
"Let Me Serenade You" – Wells
"Liar" – Hutton
"Mama Told Me (Not to Come)" – Wells
"Never Been to Spain" – Wells
"One" – Negron
"One Man Band" – Hutton sings melody with Negron on harmony on verses, then Negron takes the lead through the end refrain
"Out in the Country" – Group vocal in unison
"Pieces of April" – Negron
"Play Something Sweet (Brickyard Blues)" – Wells
"Shambala" – Wells
"Sure As I'm Sittin' Here" – Wells
"The Family of Man" – Hutton (Verse 1), Negron (Verse 2), Wells (Verse 3)
"The Show Must Go On" – Negron
"Til the World Ends" – Negron
"Try a Little Tenderness" – Wells
"Your Song" – Hutton
Considering how much of a chart commodity they were from the late 60ies to the mid 70ies, amassing countless hits and chalking up album sales of 60 million, they've really been wiped from collective memory. I know, I know, they didn't write the songs they sang, always working with outside writer material, but neither did Elvis who was the first RRHF inductee in 1986. But I guess by the 70ies you were expected to write your own material as a credible group, I'd call it the "Beatles Effect".
