Seems there was a treasure ship on its way back to port. About halfway there, it was approached by a pirate, skull and crossbones waving in the breeze!
"Captain, captain, what do we do?" asked the first mate.
"First mate," said the captain, "go to my cabin, open my sea chest, and bring me my red shirt." The first mate did so.
Wearing his bright red shirt, the captain exhorted his crew to fight. So inspiring was he, in fact, that the pirate ship was repelled without casualties.

A few days later, the ship was again approached, this time by two pirate sloops!
"Captain, captain, what should we do?"
"First mate, bring me my red shirt!"
The crew, emboldened by their fearless captain, fought heroically, and managed to defeat both boarding parties, though they took many casualties.

That night, the survivors had a great celebration. The first mate asked the captain the secret of his bright red shirt.
"It's simple, first mate. If I am wounded, the blood does not show, and the crew continues to fight without fear."

A week passed, and they were nearing their home port, when suddenly the lookout cried that ten ships of the enemy's armada were approaching!
"Captain, captain, we're in terrible trouble, what do we do?" The first mate looked expectantly at the miracle worker.
Pale with fear, the captain commanded, "First mate.... bring me my brown pants!"