horse of a different color

beat a dead horse

To persist or continue far beyond any purpose, interest or reason.

built different

Able to do things which others cannot; extremely talented or unusual.

charley horse

A muscle cramp, usually a strong one, in the thigh, leg, arm, or core.

close the stable door after the horse has bolted

To attempt to prevent a problem that has already occurred; to design and implement a preventive mechanism that is too late (after the first failure instead of before).

couldn't be more different

Two entities that have virtually nothing in common.

dark horse

Someone who possesses talents or favorable characteristics that are not known or expected by others.

different breed of cat

Something entirely different; a whole other thing or matter.

different drummer

Someone or something that implies individuality, originality, or nonconformity.