Once there was a princess, who vowed to marry the man who brought her a blue rose.

One clever suitor procured a white rose and dyed it blue. The princess admired the rose, when a bee flew into the room. It flew into the rose, and died from the poisonous fumes of the dye.
"That" said the princess, "was not a blue rose."

Her second suitor had a blue rose painted on a porcelain cup.
"It's lovely," the princess said, "But it's a cup, not a rose."

One day the young man the princess loved arrived with a white rose.
"What a lovely blue rose," the princess said.
"It's a white rose," her courtiers said.
"Oh no," said the princess. Can't you see it! It's a blue rose!"
"Yes," the courtiers agreed, "It does have a blueish tinge. I see it now."
I read the story when I was a child, and I don't remember the name of hte book. But it strikes me as the perfect definition of love.