Sometimes I think of a little story:

Once upon a time all roses were white and a symbol for innocence and purity. A girl which lived in a rich family had a big garden with only white roses.
One day the girl fell in love with a gentleman. Sadly she didn't knew he was kind of insane. After some time of their mateship they were in that garden, like many times, and the man lost his mind and murdered his lovely girl.

Because of her blood at the ground every rose in the garden became red.