Region: General | Usage example: The budget is tight, so hiring is fine, but overtime is a horse of a different color.

A horse of a different color

Meaning

A matter entirely different from the one under discussion.

Used to signal shifting to a distinct topic.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

Phrase appearing in Shakespeare's Othello to describe dissimilar things.

Cited from seventeenth century literature and still common today.