Toks said: Isn't that just a difference in romanization scheme?
Danbooru romanization uses an apostrophe (') to distinguish んい (n'i) from に (ni), so kin'iro_mosaic should be right. (The original title is "きんいろモザイク".)
This is a case where both are valid. "iro" color endings are often hyphenated, but there's also the n/i rule you noted. I use both pretty interchangeably, for this show but favor the hyphen, and since the manga uses the hyphen I'll go with that.
