I have read this somewhere and noted it for future use. Let me know if someone else have more to contribute to this list.
Black Roses signify Death
Coral Rose conveys desire
Lavender Roses symbolize love at first sight and enhancement
Orange Roses indicate enthusiasm, desire and fascination
Pink (Deep) says Thank You
Pink (Light) Rose conveys admiration, gentleness, grace, gladness, joy and sweetness
Pink Rose carry the message of happiness, gracefulness and gentleness
Red Roses symbolize sincere Love, Respect, Courage & Passion
Red (Dark) Rose reveals unconscious beauty
Red (Single) means "I Love You"
Red & White Roses together signify unity
Single Rose in any color expresses simplicity and gratitude
White Roses express Purity/heavenly, secrecy, silence, innocence and charm
White (Bridal) Rose symbolizes a happy love
Yellow Roses indicate joy, gladness, friendship and "I Care"
Yellow Rose with Red Tip indicates friendship falling in Love
The description after the color indicates how you feel about the person to whom you are sending the rose. By the way, black does not always mean that you wish the recipient to be dead; it can also be a wish for your own death, perhaps if you just can't live with the way the situation stands.