Noun
horse of a different color
(American spelling, idiomatic) An unrelated or only incidentally related matter with distinctly different significance.
For Michael Wright and Frank Darabont to cast me as the ultimate good guy and Eddie Burns as the ultimate bad guy, and really switching roles from what we usually play, is pretty awesome. That generally doesn't happen, but TNT is a horse of a different color. Neal McDonough
But that’s a horse of a different color. Source: Internet
You are welcome to do what you want to yourself, but it becomes a horse of a different color when it affects others. Source: Internet