Kermit the Frog always said it wasn't easy being green, but it's the blues that got his longtime puppeteer, Steve Whitmire, fired ... according to Jim Henson's daughter.
Cheryl Henson ripped Whitmire's on-the-job performance, saying he was making Kermit a "bitter, angry, depressed, victim. Worst of all, in the past few years he had not been funny or fun."
She says it was high time to make a change, and implored Whitmire ... "Stop with the pity party!"
Whitmire was canned last week, and bitched that Disney let him go over the phone.
The Muppets Studio issued a statement Monday, saying the official reason they pulled the trigger was "unacceptable business conduct" -- which is pretty much what Cheryl said ... with bigger words.