The Author write "彩虹屁" (Cǎihóng pì) a 'Rainbow Fart'. It means extravagant, over-the-top, often fawning praise or flattery—the kind that is so colorful and excessive it's almost ridiculous.
"Rainbow fart" is a metaphor for praise that is so effusive and flowery that it "paints a rainbow" or is as spectacular and colorful as a rainbow coming out of one's... well, rear end.
There's an existing, slightly crass but humorous concept that excessive flattery can be thought of as "farting" or producing "bullshit" (拍马屁 - pāi mǎpì, meaning "to flatter," literally "to pat the horse's butt"). So, the "fart" (屁) part of the term already had a connection to insincere or excessive praise.
The "rainbow" (彩虹) modifier takes that concept and exaggerates it to the extreme. If normal flattery is just a fart, then the incredibly elaborate, poetic, and glowing praise written by devoted fans is a spectacular, multi-colored, beautiful rainbow fart. It's so over-the-top that it transforms something base into something dazzling.
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I pluck this from The Invincible Money-Grubbing Fairy or maybe Troublemaker's Guide to Immortality? I forgot which one, but on Troublemaker's Guide to Immortality, it was when Yun Jin climb the statue and she keep sprouting rainbow farts in her mind.