(also a horse of another color American English) a completely different matter; entirely something else
یک موضوع کاملا متفاوت، یه موضوع دیگه (متفاوت با مطلب مورد بحث)
I owe you some money, I know that, but telling lie to cover for your fault has nothing to do with it. It’s really a horse of different color.
a horse of a different color
Definition of a horse of a different color
chiefly US, informal
: a very different thing or issueThat's what we'll do when he gets here. But if he doesn't show up…well, that's a horse of a different color