Определение horse of a different color в Английский Язык Английский Язык словарь
An unrelated or only incidentally related matter with distinctly different significance
Against physical danger I am willing to offer myself at any time to your Highness . . . . But to walk straight into jail, with my eyes open, that's a horse of a different color..
(Slang) entirely different subject, something that is totally unrelated (to something else), irrelevant issue